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3) Based on existing data and documents provided by the Forest Service, in <br />concert with consultation with other Forest Service staff, determine the <br />range of potential changes in water yield that could be obtained through <br />prudent management of National Forest Lands on the North Platte River <br />Basin. Any proposed silviculture prescriptions will reflect the laws, <br />regulations, and policies that empower, direct, and constrain vegetation <br />management by the U.S. Forest Service. The objective of the exercise <br />will be to optimize timber production, maintain sustainability of forest <br />ecosystem, and augment water yield. <br />A subset of objective 3 includes the simulation of the effect on water yield <br />of an extensive beetle infestation to the spruce fir type and the occurrence of <br />fire in lodgepole and ponderosa pine. <br />THE EFFECTS OF TIMBER HARVEST ON WATER YIELD; <br />OR SUMMA.RY OF OUR KNOWLEDGE <br />More than 80 years of watershed research throughout the United States, <br />much of which is specifically oriented toward the West, has demonstrated <br />,r;;::?;timber harvest, or vegetation removal, reduces net evapotranspiration (ET) <br />?, ;,rt,;:i. , <br />and results in increased stream flow (Troendle and Leaf 1980; Bosch and <br />Hewlett 1982; Callaham 1990; Stednick 1996). In the snow zone of the <br />Rocky Mountains such increases have been documented following forest <br />removal on experimenta.l watersheds at Wagon Wheel Gap (Bates and Henry <br />1928; Van Haveren 1988) and at Fool Creek (Hoover and Leaf 1967; <br />Troendle 1983; Troendle and King 1985) and Deadhorse Creek (Troendle <br />and King 1987; Troendle and Olsen 1994) on the Fraser Experimental Forest <br />in central Colorado. Other studies have shown similar responses in stream <br />flow occur following deforestation due to insect epidemics (Love 1955) and <br />fire (Troendle and Bevenger 1996). The magnitude of the observed changes <br />in flow in the snow zone is similar in nature to those observed elsewhere in <br />forested environments for similar levels of impact; although the distribution, <br />or timing, of the flow change is more reflecrive of the dependence on snow <br />melt (Troendle and Leaf 1980; Troendle and Kaufinann 1987; Troendle, et <br />al. 1998). The sub alpine environment is also unique both in terms of the <br />time of year when the flow change occurs, and in the persistence, or <br />longevity, of the treatment effect (Troendle and Leaf 1980; Troendle and <br />King 1985; Troendle and Kaufinann 1987). <br />? <br />?\....._...2 <br />