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Managing Arid and Semi-Arid
Watersheds
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The Beaver Creek Biosphere Reserve |
About the ProgramAmericans look to their public forest and rangelands to fill many of their basic needs for water, food, energy, shelter, and clothing. Demands for these goods are more intense and diverse than ever before. At the same time, more and more people turn to public lands for recreation, relaxation, and educational experiences. Public land managers must respond to people's needs while maintaining the quality and productivity of the environment. Consequently, better ways are being sought to assess and select management practices that will yield reasonable combinations of products such as wood, water, or livestock forage; as well as provide other values such as wildlife habitat, scenic beauty, and recreation opportunities. For example, practices that emphasize water and forage production may reduce wood supplies and compromise the quality of habitat for some animals. Emphasizing timber production might lower scenic beauty, but improve habitat for big game animals.
The goals of the Beaver Creek Program are to provide land managers with: (1) essential facts about the biological, physical, social, and economic effects of multiresource management actions in ponderosa pine forests and pinyon-juniper woodlands; and (2) better ways to predict, display, and evaluate differences among the probable results of management alternatives before actions are initiated. A Cooperative EffortMany organizations are involved in this program, including several Forest Service research and management units, other federal and state agencies, universities, foundations, and private concerns. Their varied skills and expertise are vital to its success. Program EvolutionIn the summer of 1955, several ranchers met with a Forest Service representative and an officer for the Salt River Project, an organization of water users in southern Arizona. The ranchers and the water users' agent were concerned that increasing numbers of trees and shrubs were reducing the flow of streams and the supply of livestock forage on watersheds in the State. As a result, the University of Arizona was commissioned to investigate the potential for improving water yield from the State's forests and ranges. University findings, titled Recovering Rainfall, better known as the Barr Report, suggested that surface water runoff from mountain watersheds might be increased by replacing high water-using plants, such as trees and shrubs, with low water users, such as grass. Based on this report, the Forest Service began to test theories for increasing the flow of mountain streams. By 1960, studies dealing with ponderosa pine and pinyonjuniper lands had evolved into the Beaver Creek Watershed Evaluation Program. Its emphasis was to determine how much water yield could be increased using various methods for altering the vegetation. Changes in livestock forage, timber production, wildlife habitats, recreational values, and soil movement also were to be studied. Similar projects were undertaken by other Forest Service units in areas of mixed conifer, chaparral, and streamside vegetation elsewhere in Arizona. Results of studies conducted to date at Beaver Creek, and other locations, show that changes in plant cover can produce substantial streamflow increases from some vegetation types, but not all. The impacts of watershed management practices on other range and forest resources also have been assessed. Getting the Project RollingBetween 1957 and 1962, 20 specific watershed study units within the Beaver Creek area were designated to test the effects of several vegetation management practices on water yield and other resources. Of the 20, 18 were watersheds from 66 to 2,036 acres where specific vegetation modifications could be tested on a pilot basis. The other two—encompassing 12,100 and 16,500 acres—were watersheds set aside to demonstrate the effects of management practices on areas of the size forest managers work with daily. Recently, 24 smaller watershed units, each having uniform soil, plant life, and topography, were defined in areas of diverse ecological characteristics. Information from these units helps refine and verify findings—from studies on the larger watersheds—for use over a wide range of conditions. Measuring Results of TreatmentsBefore any vegetation was changed, runoff from each watershed was measured for several years to determine streamflow variations under pretreatment conditions. During this time, the quantity and quality of other natural resources also were inventoried. With pretreatment measurements completed, six watersheds—Bar-M and Watersheds 2, 5, 13, 15, and 18—were designated as untreated "controls". They were shown to respond to environmental influences in a manner similar to the watersheds where experimental treatments would be applied. Measurements continue on both experimental and control watersheds for several years after treatments are applied. Streamflow, sediment production, and water quality are monitored regularly, and other resources are reinventoried periodically. Changes caused by the management practices applied to the experimental units are evaluated by comparing posttreatment values with pretreatment data and with data from the untreated "control" watersheds. Pinyon-Juniper Treatments and ResultsThe pinyon-juniper experiments were among the first conducted in the Beaver Creek area. Prior to these studies, many woodland managers thought pinyon-juniper removal would improve both streamflow and forage production. Large areas throughout the Southwest had been cleared expecting these benefits. However, results at Beaver Creek show that substantial forage increases are possible, but that changes in water yield are not likely to be significant. Three techniques were used to remove pinyon and juniper trees from Watersheds 1, 3, and 6—uprooting, herbicide spraying, and cutting, respectively. Herbicide spraying on Watershed 3 was the only treament to yield a significant streamflow increase. However, the government carefully controls the use of herbicides for environmental reasons, limiting the general use of this technique. Mechanical removal, such as uprooting or cutting, is the primary means for converting pinyon-juniper woodlands to other types of vegetation. Increased grass is the most noticeable change triggered by pinyon-juniper removal. However, the cost of removal usually is more than the value of the livestock forage gained unless the trees can be sold for fenceposts or firewood. Pinyon-juniper removal also causes wildlife changes, particularly among small mammals and birds. For example, birds that feed in trees are replaced by ground feeders. The predominant game animal—the mule deer—is affected little by tree removal when woodland cover is left not far from the openings. However, more forage is made available in early spring when deer often need additional nourishment. Records from the pinyon-juniper watersheds show that erosion rates and sediment loads in the streams have varied sharply with the intensity of storms. A heavy storm soon after the trees were removed from one watershed washed away much soil. In the long run, however, average sediment loads from the treated watersheds do not exceed those from the control watersheds significantly. On watershed 3, herbicide residues found in small amounts in streamflows the year following application soon disappeared. On all three watersheds, changes in water quality have been minor. ConclusionThe work centered at Beaver Creek is one example of the Forest Service responding to changing public and environmental needs. Basic knowledge about environmental interactions continues to flow from the watershed experiments begun years ago. Resource management planning methods being developed and tested are helping public land managers to better assess the status and future of the resources under their supervision and to plan and implement appropriate management programs. Results from this research and testing program should provide continuing assistance to natural resource agencies and industries as they respond to America's changing demands for forest and range products and outdoor experiences. The Beaver Creek Watershed is still a designated biosphere reserve and, as such, continues to function as an outdoor laboratory, providing study areas for various research cooperators. Those interested in exploring these opportunities should contact the Rocky Mountain Research Station, USDA Forest Service, Flagstaff, Arizona. For more information about upcoming workshops on the Beaver Creek Watershed, contact The University of Arizona Cooperative Extension office in your county.
If you have questions or need assistance, contact: USDA Forest Service or Forest Supervisor |
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