Sierra Ancha Experimental Forest

Results, Implications, and Current Status

Results

Earlier status-of-knowledge publications presented the results of increasing water yields and other multiple use values in chaparral shrublands through the early 1970s (Brown et al. 1974, Cable 1975, Hibbert et al.1974). These results have been refined and, in some cases, expanded upon in subsequent publications (Gottfried et al. 1999, DeBano et al. 1999a, and DeBano et al. 1999b). Important findings are presented below; details are found in the cited literature.

Conclusions from the Base Rock Lysimeters showed that (Martin and Rich 1948):

• 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 thunderstorms.
• 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 plots.
• 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 vegetation
• An increase of 22% in streamflow occurred on treated areas (Ingebo and Hibbert 1974). Pretreatment average annual streamflow was 1.65 inches.
• 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 1983).
• 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 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.

Implications

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.

Current Status

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 future contributions.