Sierra Ancha Experimental Forest Watersheds - Treatments
Short-term studies were used to investigate hydrological and ecological
relationships of different plant communities found on the Sierra Ancha
Experimental Forest. The results of these studies provided the basis for
establishing long-term watershed studies to more fully evaluate water
yield responses to brush control in chaparral (Natural Drainages), and
to timber harvesting (Workman Creek) in mixed conifer forests. Studies
were designed to test erosion control and revegetation techniques (Hendricks
1936, 1942, Hendricks
and Grabe 1939). Cooperrider
and Hendricks (1940) and Hendricks
and Johnson (1944) studied the effects of grazing or wildfire on soil
(1938) and Cooperrider
et al. (1945) evaluated winter hydrographs for both Parker Creek and
the Salt River.
Watershed treatment in mixed conifer vegetation
Low density chaparral vegetation
The effect of consumptive use of range vegetation on soil and water resources
was determined by using small lysimeters. A lysimeter is an instrument
for measuring the amount of water percolating through soils and for determining
materials dissolved by the water. Evaporation from bare soil was compared
to evapotranspiration from perennial grasses and shrubs (Rich
and Rich (1955) developed a method of classifying southwestern watersheds
on the basis of precipitation, potential evapotranspiration, and potential
water yields. Most water yields result from water stored in the soil during
the winter when evapotranspiration is low. High water yielding areas
should be managed for water augmentation while intermediate and low-water
yielding areas should be managed to reduce erosion.
Watershed assessments suggested that streamflow was related to the interaction
of precipitation and the different native vegetation types occupying the
upland watersheds of the Salt River Basin (Cooperrider
and Sykes 1938, Cooperrider
and Hendricks 1940, and Cooperrider
et al. 1945). This finding encouraged further research on techniques
of vegetation manipulations and the hydrologic responses to these manipulations.
Of particular interest was development of a method for controlling deep-rooted
brush species and replacing them with shallower-rooted grass plants.
Short-term studies were also conducted at Workman Creek to supplement
information gained from watershed-level studies. Investigations were conducted
on the control of New Mexico locust and Gambel oak (Gottfried
and Gottfried 1983). The biomass of locust, both above-and below-ground,
was also related to water yield (Gottfried
and DeBano 1984). Another concern of managers was the potential impact
of pocket gophers on ponderosa pine seedling survival (Gottfried
and Patton 1984).
Important study areas dedicated to long-term research were located at
the Base Rock lysimeters, Natural Drainages (watersheds), and the Workman
Base Rock Lysimeters
Hydrologic research in the 1930s used lysimetry to obtain quantitative
information on the water balance for different vegetation types, because
it offered a degree of experimental control that was not attainable using
experimental runoff plots or small and large watersheds (Martin
and Rich 1948). However, limitations associated with the use of lysimeters
were recognized. Typical limitations include difficulty on making the
lysimeters of sufficient size to reduce border effects and the disruption
or destruction of the natural soil profile. The lysimeters constructed
on the experimental forest mitigated these limitations by using large,
undisturbed soil blocks overlying bedrock and, therefore, were named the Base Rock Lysimeters. Three lysimeters (18 ft wide and 50 ft long)
with undisturbed soil profiles were established on an area supporting
a deteriorated stand of perennial grasses, snakeweed (Gutlerrezia sarothrae)
and yerba-santa (Eriodictyon angustifloium) (less than 2% total
plant cover). Revegetation treatments including seeding, fertilizing and
watering the lysimeters were carried out during 1934 and 1935. By 1942,
the cover had increased to about 8% and consisted of mainly sprangletop
(Leptochioa dubia), and sideoats (Bouteloua curtipendula)
and hairy grama (Bouteloua hirsuta). Three grazing treatments applied
between 1942 and 1948 were:
Overgrazing with sheep at the rate of 2 mature ewes for 4 days annually,
usually in October.
The major portion of annual water yield occurred during winter as
sub-surface flow from long-duration, low-intensity storms.
Most surface run-off and soil erosion occurred during summer storm
events from short-duration, high-intensity thunderstorms.
Overgrazing caused increases in summer surface runoff and erosion
and decreases in areal infiltration capacities, while the amount of
winter water percolation was independent of the grazing treatment. Soil
losses during summer storms increased from 60 to 307 tons/mi2 on heavily
grazed plots compared to the ungrazed controls. In contrast, winter
soil losses only increased from 15 to 68 tons/mi2 on moderately grazed
Results from late summer frontal-type storms were intermediate between
those from summer and winter storm events.
Four chaparral-covered watersheds, called the Natural Drainages, were
established on the Sierra Ancha Experimental Forest in 1934. These watersheds
ranged in size from 9 to 19 ac. Precipitation and runoff were measured.
The upper slopes of the watersheds are covered with diabase soils, which
cover between 28 and 54% of the watersheds. Soils on the lower slopes
were derived from quartzite. The original vegetation on these watersheds
was sparse, with low density chaparral stands on southerly exposures.
Before treatment, crown cover of the chaparral shrubs was 20 to 25% compared
with covers two-to-three times this density on the Whitespar and Three
Bar watersheds (DeBano
et al.1999a and DeBano
et al.1999b). Shrub live oak was the most abundant shrub. Livestock
grazing first started about 1880 and continued until 1934, when experimental
watersheds were established on the Sierra Ancha Experimental Forest.
The Natural Drainages were one of the first watershed-level studies used
in the Central Arizona Highlands to evaluate the effect of grazing on
vegetative change and on production of streamflow and sediment. Two of
the four watersheds were grazed by cattle and horses for short periods
during the fall and spring beginning in 1939, and 2 watersheds were the
and Reynolds 1963). Herbaceous vegetation was quantified using meter-square
quadrants. Streamflow and sediment was measured using 90° V-notch
weirs and sediment was measured in weir basins at the bottom of each of
the 4 watersheds. These studies were terminated in 1952 when it was determined
that the intensities of grazing used in the studies had no effect on total
water yield or sediment trapped in the weir ponds (Rich
and Reynolds 1963).
A growing interest in augmenting streamflow in the Central Arizona Highlands
by manipulating native vegetation developed among water users in central
Arizona during the 1950s. As a result, many of the research efforts during
this period were initiated to evaluate the feasibility of increasing streamflow.
A second experiment designed to determine the effects of chaparral cover
manipulations on streamflow was started on the Natural Drainages in 1954
and Hibbert 1974). Chaparral cover was suppressed on 2 watersheds
by treating the shrubs with herbicides, while the other 2 watersheds were
maintained as control areas.
Overall, major amounts of sediment-free water come from areas with good
grass cover and soil erosion is greatest where vegetation densities have
been decreased, as by overgrazing.
Results from herbicide studies on the Natural Drainages watersheds indicated:
There was 3-times more grass, forb, and half-shrub production on
the treated areas having quartzite soils than on similar soils on the
control areas (Pond 1964). No differences in plant production were observed
on the diabase soils.
An increase of 22% in streamflow occurred on treated areas (Ingebo
and Hibbert 1974). Pretreatment average annual streamflow was 1.65
The treated areas showed a 30% increase in quickflows, a 32% increase
in delayed flows (the rising and falling stages of a streamflow hydrograph),
and a 26% increase in peak flows (Alberhasky
A decline of 72% in annual sedimentation was attributed to the increase
in grass cover on the treated areas.
Streamflow increases from vegetation manipulations were attributed to
lower evapotranspiration demands by the replacement grass cover. The streamflow
increases from the Natural Drainages watersheds were low compared to other
chaparral areas (Hibbert
et al. 1974); this was related to the initial low density of shrubs
and to the southeastern exposure of the area that results in relatively
high energy inputs for evapotranspiration.
Workman Creek Watersheds
A major project was conducted on the Workman
Creek watersheds to evaluate the hydrology of higher elevation mixed
conifer forests, and to determine the changes in streamflow and sedimentation
resulting from manipulating the forest vegetation.