Results, Implications, and Current Status
After a wildfire in 1959, Watershed D recovered naturally to be used
as a control and Watershed B, Watershed C, and Watershed F received chemical
treatments. Results of the treatments were:
- The effect of the wildfire on streamflow was generally short-lived.
A sharp increase in overland flow occurred the first few years after
the wildfire, especially during the first summer rains.
- Stream flows increased on all the Three-Bar watersheds. However, after
the third year, the crown cover on the control watershed (Watershed
D) was dense enough to prevent any increased water production.
 
Wildfire
Following the treatment on Watershed C:
- Stream flow increased four-fold (5.8 area-inches of water) over a
11 year period when compared with flow from the control watershed D.
 
- Foliar herbicides killed about 40% of the shrub live oak and 70% of
the birchleaf mountainmahogany. Because of the poor rate of shrub control,
the remaining shrubs were treated individually with soil-applied herbicides
in 1965 and 1968, which reduced the shrub crown cover to less than 3%
by 1969.
- Annual forage production averaged 1,200 lb/ac, and provided a ground
cover which maintained high infiltration rates.
- The increase in streamflow, and particularly yearlong streamflow,
allowed riparian stringers to become established below the gaging station
(DeBano et al. 1984).
 
- Bird populations flourished in the newly created riparian stringers,
but were reduced in the areas converted to grass (Szaro 1981).
Results from Watershed B were:
- Nitrates in streamflow rose to relatively high concentrations (about
85 ppm) and was exported from the watershed in amounts up to 125 lb/ac/yr,
in comparison to a control watershed value of about 1 lb/ac/yr. High
concentrations of nitrates in the streamflow persisted longer from the
two?stage treatment on Watershed B than from the one-stage treatment
on Watershed F. High nitrate concentrations (44-373 ppm) were found
in soil solutions from 5, 10, and 15 ft depths on the converted watershed
as compared to low nitrate concentrations (0.2-6.2 ppm) on an adjacent
undisturbed area (Davis 1987a, Davis and DeBano 1986).
- Herbicide (picloram) concentrations in streamflow were higher (360
to 370 ppb) during the initial three months following treatment than
thereafter. After 14 months and 40 inches of accumulated rainfall, picloram
could not be detected in the streamflow (Davis 1973).
- Surviving chaparral shrubs were re-treated in 1968 and again in 1978
(Davis 1987a). These additional two treatments reduced the shrub cover
to about 8%.
- Annual grass and forb production averaged 690 lb/ac on the treated
areas as compared to 300 lb/ac on nearby untreated slopes.
 
Results from Watershed F were:
- Nitrate concentrations in streamflow from the control (watershed D)
remained less than 1 ppm, while nitrate from the treated watershed increased
to a maximum concentration of 56 ppm during the first posttreatment
year, with an annual concentration of 16 ppm (Davis 1984, 1987b, 1989).
- Shrub crown cover was reduced from 55% to less than 5% the first year
after treatment. Shrub kill increased to more than 95% after two years.
- Runoff efficiency (the ratio of streamflow-to-precipitation) was increased
to 2.3 times the efficiency of the control watershed (Watershed D),
which amounted to an increase of 1.5 area-inches of streamflow.
Other Studies
Results of other studies near the Three-Bar experimental watersheds,
and conducted elsewhere in the chaparral shrublands in the Salt-Verde
River Basin are summarized below. In addition to testing of the effectiveness
of herbicides for shrub control, other studies using prescribed fire and
biological control (goat browsing) were tested.
When using fire, more than one-half of the chaparral canopy should be
eliminated and prevented from becoming re-established, to obtain relatively
high levels of seeded grass production (Pase 1971 and Pond 1961). However,
burning can also result in an increase in undesirable plant species (Pase
1965).
Goat browsing reduces total cover in chaparral stands, particularly when
done in conjunction with initial brush-crushing (Severson and DeBano 1991).
Goat browsing to control chaparral shrubs can generally be expected to
result in the consumption of the same plant species that would be preferred
by cattle, deer, and elk (Knipe 1983). Successful use of goats to control
shrub requires an intensive level of animal management.
The root system of a shrub live oak was excavated to characterize its
mass (Davis and Pase 1977). It was determined that:
Shrub live oak root system
- The root system included a taproot, many deep-penetrating roots, and
profuse lateral roots.
- The shrub live oak root system is able to effectively deplete both
ephemeral surface and deeply stored soil moisture.
A study was conducted on the west side of Lake Roosevelt and north of
the Three-Bar Wildlife area, to measure the temporal and spatial sediment
delivery to and within a stream network following a wildfire in chaparral
shrublands. This study indicated that:
- Severe erosion following a wildfire deposited large amounts of hillside
soil and debris in the channel system (Heede 1988).
- As vegetation recovery after fire, sediment delivery from the watershed
practically ceased.
- Relatively clear water, upon entering the channel, caused degradation
of the sediment deposited in the tributaries, and delivered this sediment
into the main channel for many years after active hillslope erosion
on the watershed had ceased.
- The delayed sediment delivery over time made it difficult to interpret
the effect of current management activities on erosion responses.
Mule (Odocoileus hemionus) and white-tailed deer (O. viginianus), and
black bear (Ursus americanus) were studied on the Three-Bar Wildlife Area
by the Arizona Game and Fish Department. These studies indicated that:
- Mule and white-tailed deer select a variety of plants for food, including
forbs, dwarf and half-shrubs, mast and other fruits, and evergreen browse
of both chaparral and desert shrub (McCulloch 1973, Urness 1973, Urness
and McCulloch 1973).
- While conversion treatments increased forage production for cattle,
they had adverse effects on deer, particularly when conversions of large
areas, or entire watersheds, were implemented (McCulloch 1972).
- Cover and food for black bear are enhanced in habitats composed of
shrubs and low trees interspersed with a few forest species in the major
drainages. This arrangement provides numerous mast- and fruit-producing
species (LeCount 1980).
- Leaving areas of adequate size as escape cover, and providing a number
of seral stages of postburn vegetation should benefit both game and
nongame wildlife species (Pase and Granfelt 1977). Less than one-half
of the area should be converted (Reynolds 1972).
An inventory was made of 139 chaparral sites totaling almost 335,000
ac was accomplished in the early 1970s (Brown, T.C. et al. 1974). The
costs of converting portions of chaparral shrubland areas that met crown
cover, slope, and managerial criteria for conversion to grass, and maintaining
these conversions over 50 yr, was compared with the benefits to society
in terms of increased water yield and forage for livestock, and reduced
fire-fighting costs. It was shown that:
- Using fire as the main conversion tool, 96 of the inventoried sites
(69%) had a benefit-cost ratio greater than 1. Using a soil-applied
herbicide, 72 sites (52%) met that economic criteria.
- Proper management would favorably affect soil movement, wildlife habitat,
and esthetics. Recreation use would be unaffected in most treated areas.
Implications
Information has been obtained on how chaparral shrubland ecosystems function
for land management decision making. Past research has contributed information
on shrub control techniques, watershed and soil responses to shrub control,
water quality, wildlife habitat changes, and economics. The most important
management implication of this research is the ability to determine how
to control chaparral shrubs to enhance the production of water and forage
and to maintain wildlife habitat diversity.
If chaparral shrub suppression is desired, burning must be combined with
other control methods such as applications of soil-applied herbicides
or mechanical control methods. A problem associated with mechanical equipment
is that it is limited to slopes with less than a 10% grade on rock free
soils. One advantage of using prescribed fire is that the environmental
changes created are similar to those occurring during the natural evolution
of fire-adapted ecosystems. A disadvantage of using prescribed fire is
that shrub control is temporary. Therefore, a management objective is
often the suppression of shrubs rather than their eradication.
Current Status
Hydrologic evaluations on the Three-Bar watersheds were discontinued
in 1983. The Three-Bar Wildlife Area remains ungrazed and provides a study
site for current wildlife studies and for monitoring by the Arizona Game
and Fish Department.
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