Whitespar Watershed B

AREA: 246 ac ( ha)
SLOPE:
ASPECT: Southeast facing
ELEVATION: 5,900 to 7,200 ft (1,800 to 2,195 m)
VEGETATION: Chaparral-dominant shrubs are shrub live oak and true mountainmahogany (crown cover considered medium density, 50 to 60 %).
PARENT MATERIAL: Fine-grained granite
GAGE: 120° V-notch
PERIOD OF RECORD: 1958 through 1983

OBJECTIVE: To determine how converting chaparral vegetation to grass affects streamflow, erosion and sedimentation, vegetation, and wildlife. Prior to treatment, streamflow from WSB was calibrated against streamflow from the designated control WS A. Streamflow was ephemeral on both watersheds prior to treatment.

TREATMENT: Conversion of channel-side brush in 1967 to grass was the first of a series of treatments to eventually convert the entire watershed (Hibbert et al. 1974). The intent of this chemical treatment was to eliminate all shrubs and juniper trees using water from the moist channel environment. By eliminating these plants, water concentrating along the stream channel would be subject to less transpiration loss before contributing to streamflow. Bounds of the treated zone were set at 30 vertical feet above and no more than 75 feet horizontally from the channel. Due to the lack of perennial stream flow, plant cover in the channel zone was not what is considered typically "riparian". There were no sycamore, alder, cottonwood, or other species often found along streams.

The treatment covered 38 acres, 15 % of the watershed. Pelleted fenuron (25 % active ingredient-ai) was placed by hand underneath shrubs and small junipers in March 1967 (Hibbert et al. 1974). The average rate of application on the 38 acres was 23.2 pounds (ai) per acre. Intershrub spaces were not treated to avoid killing grasses and forbs.

The second treatement was made in 1973 to convert an area of similar acreage on the upper slopes in a strip surrounding the watershed just inside the boundary to simulate a fuel break.

RESPONSES: The single application of fenuron gave 80 to 90 % control of the shrubs eliminating need for further treatment of the area (Hibbert et al. 1974). The native grasses and forbs increased substantially on the treated area, providing good cover except in the patches of Gambel oak where establishment of grasses and forbs was slow. Cattle graze both watersheds, although B was fenced after treatment to control grazing.

During the second and particularly the third summer after treatment, flannel mullein (Verbascum thapsus) a disturbance species flourished along the moist channel bottoms. By the fifth growing season these plants were no longer numerous. Since flow increased throughout these years, it is apparent that the vigorously growing weeds did not consume as much water as the brush.

More details of treatments and treatment response can be found in Hibbert and Ingebo 1971, Hibbert et al. 1974, and Ingebo 1971 and 1972.

SELECTED REFERENCES

Hibbert, Alden R. and Paul A. Ingebo. 1971. Chaparral treatment effects on streamflow. p. 25-34. In 15^th Annual Arizona Watershed Symposium, Phoenix, AZ, September 1971, 15:?????.

Hibbert, A.R.; Davis, E.A.; Scholl, D.G. 1974. Chaparral conversion. Part I: Water yield response and effects on other resources. USDA Forest Service Research Paper RM-17, 36 p. Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO.

Ingebo, Paul A. 1971 Suppression of channel-side chaparral cover increases streamflow. Journal of Soil and Water Conservation 26:79-81.

Ingebo, P.A. 1972. Converting chaparral to grass to increase streamflow. Hydrology and Water Resources in Arizona and the Southwest. 2:181-192.