The Whitespar watersheds were treated in 3 phases reflecting the changing
emphasis on chaparral management over time. Each treatment phase required
a pretreatment stream discharge calibration period lasting several years
to establish the annual runoff relationship between the control and the
treated watershed. The 3 treatment phases on Whitespar A and B were experiments
designed to address emerging questions.
The Phase 1 experiments were applied to Whitespar B in the 1960s
to determine whether annual streamflow could be increased by killing the
chaparral brush and trees in and along the main channel (essentially
a riparian treatment). Previous studies in California indicated that
clearing trees along channels would substantially decrease evapotranspiration
and increase streamflow. The main emphasis in the 1950s and early 1960s
was managing chaparral vegetation to produce water yield increases. The
riparian areas throughout the Central Arizona Highlands were viewed as
major consumers of available water, causing reduced streamflow. Conversion
of these woody riparian species to grass or other species that use less
water was promoted. A decade later, these riparian systems were recognized
as important recreation sites and wildlife habitats that required preservation
and enhancement to maintain their sustainability.
Within the context of earlier research emphasis on riparian treatment,
37 acres (about 15% of the watershed) of the channel area were treated
with soil-applied herbicides that was hand applied underneath shrubs and
small junipers in March 1967. Intershrub spaces were not treated to avoid
killing grasses and forbs. Larger junipers were either cut or girdled.
The single application of the soil-applied herbicide gave 80% to 90% control
of the shrubs and made a follow-up treatment unnecessary. The channel
treatment effect was evaluated for 7 yr, after which the Phase 2 experiment
The Phase 2 experiment began in 1973 with a second treatment on
Whitespar B. This experiment was started after the effect of the channel
treatment on streamflow had stabilized and been evaluated. The objective
of the Phase 2 experiment was to determine whether ridgeline brush-control
would affect annual streamflow volume. The treatment consisted of treating
the boundary ridges and a main centrally-located ridge with soil-applied
herbicides broadcast aerially. A follow-up treatment was necessary in
1976 because of uneven chemical distribution and poor shrub control after
the aerial application. The overall shrub reduction on the areas treated
was about 85%. The combined area was about 20% of the watershed (49 acres).
The evaluation was for 7 yr.
The Phase 3 experiment was the last applied on the Whitespar watersheds.
In February 1981, soil-applied herbicides were applied by helicopter in
a mosaic pattern on Whitespar A. The treatment was applied to about 55%
of the watershed (168 acres). This treatment pattern was designed to incorporate
what had been learned from previous experiments into a design that would
increase water yield without degrading wildlife habitat or other watershed
resource values. Hydrology, soil-plant water relations, and wildlife habitat
improvement were considered in designing a mosaic conversion pattern on
Whitespar A that was aesthetically pleasing and technically feasible to
implement by applying herbicide with a helicopter. Because of esthetics
and wildlife values, all ponderosa pine and Gambel oak stands were excluded
from treatment. The ponderosa pine sites were used extensively for roosting
doves and pigeons and contained big game trails leading into the watershed.
Gambel oak sites along stream channels are valuable javelina (Tayassu
tajacu) and deer habitat.