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Water scarcity presents a crucial challenge for water resource managers charged with maintaining hydrologic resources for domestic, industrial, and agricultural use while protecting natural systems. While the perceived benefits of forest management are often limited to habitat improvement, specific management actions that reduce forest biomass (from thinning and prescribed fire) may also have implications for regional water yield. Because evapotranspiration (ET) dominates ecosystem water losses, even modest reductions in the proportion of rainfall lost to ET (e.g., from 90% to 80%) can result in large fractional increases (e.g., doubling) in water yield. It follows that forest biomass reduction by land management agencies and private or industrial landowners should increase water subsidies to surface water and groundwater resources. To reduce uncertainty around projected water yield subsidies from modified management we are applying a comparative evaluation of the effects of land management on forest biomass, ET, and water yield across a gradient of environmental conditions (soil type, aquifer confinement, and climate). Within each site, treatments target variation in management activities (e.g., thinning, clearcutting, and fire) and forest biomass. Groundwater and soil moisture data are used to construct daily vadose zone and aquifer water budgets to determine ecosystem ET and water yield, while forest structure is evaluated via measurements of leaf area index (LAI), which has been shown to regulate stand ET and is directly related to management strategies. These data will then be used to derive specific management-water yield relationships to guide watershed-scale strategies for sustaining regional water resources. |