Watershed Research and Education
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Watershed 8

Area: 1,802 ac (730 ha)
Elevation: 6,900 TO 7,685 ft (2,104 to 2,344 m)
Vegetation: Ponderosa Pine
Parent Material: Basalt
Years: 1957 - 1983
Treatment: Silvicultural thinning
Year Treated: 1974

Untreated ponderosa pine stands
Untreated ponderosa pine stands
Objective: To determine how a silvicultural thinning of ponderosa pine affects streamflow, erosion and sedimentation, vegetation, and wildlife. Prior to treatment, streamflow from WS 8 was calibrated against streamflow from the designated control WS 13.
Treatment: In 1974, this forest was thinned to 70 percent of its original density. Trees removed depended largely on the age of the individual stands. Slash and small trees that could not be sold were piled and burned. This management technique is designed to stimulate tree growth and maximize future timber yields. For that purpose, periodic thinning harvests would be scheduled every 20 years, with new trees naturally replacing those removed. When enough facts are collected and analyzed, it is anticipated that this treatment will show greater timber yield potential than those applied to WSs 14 and 17.
Response: The first 2 years of streamflow response on the lightly cut watershed were 32 mm (20%) and 44 mm (28%), respectively. Response in these years appear comparable in relative magnitude to the 100 percent and 77 percent treated watersheds and are followed by the larger responses of 108, 102, and 80 mm in 1978, 1979, and 1980, respectively, which were much wetter years. The 1980 response of 80 mm is different from the negative or low responses observed on WS 12 and 17. Water year 1980 had major streamflow production in January and February which amounted to 70 % or more of the annual streamflow total on all but the lightly cut watershed. On WS 8 only 40 % of the annual total occurred in January and February and another 40 % occurred in April. This is a prime example of how streamflow timing or distribution can influence the annual streamflow total.
References: Baker, M.B., Jr. 1986. Effects of ponderosa pine treatments on water yield in Arizona. Water Resources Research 22: 67-73.

Brown, H.E., M.B. Baker, Jr., J.J. Rogers, W.P. Clary, J.L. Kovner, F.R. Larson, C.C. Avery, and R.E. Campbell. 1974. Opportunities for increasing water yields and other multiple use values on ponderosa pine forest lands. USDA Forest Service, Research Paper RM-129.
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