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.
TreatmentsThree techniques were used to remove pinyon
and juniper trees from Watersheds 1, 3, and 6uprooting, 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
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.
Sediment basin splitter #1, Beaver Creek Watershed
ResultsIncreased 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 animalthe mule deeris
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
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.