MODERATE TIMBER HARVESTING INCREASES WATER YIELDS FROM AN ARIZONA MIXED CONIFER WATERSHED1

: A paired watershed design was used to evaluate the effects of a management prescription which included patch clearcutting, group selection, and singletree selection harvesting on water yield improvement. The harvest created 63 openings, averaging 0.5 ha in size over 13 percent of the watershed area. Stand density was reduced by 34 percent to 30 m2/ha. Average annual streamflow for the initial eight-year period since treatment increased significantly by about 45 percent, or 44 mm, mostly because of increased winter runoff. A greater proportion of the snowmelt-generated streamflow occurred earlier in the spring, while annual peak flows were increased by an average of 65 percent, or about 28.42 1/s/km2. Maximum snow water equivalents remained unchanged. The primary causes of the increases were reduced evapotranspiration and increased snow accumulation in the openings; however, it appears that the partially cut stand contributed to the increases.