Pinyon-Juniper Woodlands

Treatments and Results

The 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. A paired watershed approach was used to determine water yield responses. Treatments—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.

Sediment basin splitter #1, Beaver Creek Watershed 1

According to Hibbert (1979), little opportunity exists to reduce transpiration where precipitation is less than about 18 inches (460 mm) and is exceeded by potential evapotranspiration (warm, dry portions), because precipitation does not penetrate far into the soil, and one vegetation type is about as efficient as another in using the available water. Most pinyon-juniper woodlands receive 18 inches or less presipitrtion annually.

Results—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.