The major portion of annual water yield occurred during winter as
sub-surface flow from the long-duration, low-intensity storms.
Most surface run-off and soil erosion occurred during summer storm
events as a result of the characteristic short-duration, high-intensity
Increases in summer surface runoff and erosion and decreases in areal
infiltration capacities resulted from overgrazing, while the amount
of winter percolation appeared to be independent of grazing treatment.
Soil losses during summer storms increased from 60 to 307 tons/mi2 on
heavily grazed plots compared to 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 appeared to be intermediate
between those of summer and winter storm events.
Overall, major amounts of sediment-free water come from areas with good
grass cover and that 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 three-times more grass, forb, and half-shrub production
on the treated areas having quartzite soils than on similar soils on
control areas (Pond 1961). No differences in plant production were observed
on the diabase soils.
Low density chaparral
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 quick-flows, 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 Natural Drainages were low compared to other chaparral
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.
Research on the Sierra Ancha Experimental Forest has contributed to the
knowledge base of hydrology, watershed management, and basic ecology for
over 65 years. These studies provided:
Guidance for subsequent watershed research programs in chaparral
and mixed conifer forested ecosystems.
Information on water yield responses to vegetation manipulation that
is useful to land managers and researchers.
Research findings that continue to be implemented when designing
multiple resource ecosystem management treatments.
Most of the hydrologic measurements on the Sierra Ancha Experimental
Forest were discontinued in the late 1970s and 1980s in response to a
shift in USDA Forest Service research priorities. Currently, only the
Upper Parker Creek weir, the Sierra Ancha weather station, and the USDA
Natural Resources Conservation Service snow measuring station are active.
Ecologically-oriented research continues to a limited extent.
Arizona State University entered into a lease agreement with the Forest
Service in 1983 to use the Parker Creek Headquarters complex. The experimental
forest and surrounding Tonto National Forest continues to be used for
faculty and graduate student ecological research and summer field classes.
The Parker Creek complex is used for Forest Service, university, and conservation
group meetings. The Sierra Ancha Experimental Forest has a tradition of
natural ecosystem ecology and management research and the potential for