In the early 20th century, watershed managers became concerned that erosion
on the adjacent and headwater watersheds of the Salt River would move
sediment into the newly constructed Roosevelt Reservoir and decrease its
capacity. Measurements indicated that 101,000 ac-ft of coarse granitic
sediments accumulated behind Roosevelt Dam between 1909 and 1925. The
Summit Plots, located between Globe, Arizona and Lake Roosevelt, were
established in 1925 by the USDA Forest Service 15 mi upstream from Roosevelt
Dam to study the effects of vegetation recovery, mechanical stabilization,
and cover changes on stormflow and sediment yields from the lower chaparral
zone (Rich
1961).
Shortly after establishing the Summit Plots, the USDA Forest Service
dedicated a research area known as the Parker Creek Experimental Forest
in May 1932 (Gottfried
et al. 1999, USDA
Forest Service 1932). This experimental forest was enlarged and renamed
the Sierra Ancha Experimental Forest in April 1938 (Fig. 3). Numerous
hydrologic and ecological experiments that were conducted on the Sierra
Ancha Experimental Forest.
Other studies began in the 1950s with the establishment of the Three
Bar watersheds in chaparral vegetation on the west side of the Tonto Basin
(Hibbert
et al. 1974, DeBano
et al.1999a). The initial research objective of the Southwestern Forest
and Range Experiment Station (currently the Rocky Mountain Research Station)
was to develop a program to study the interrelated influences of climate
and soils, topography and geology, and the nature, condition, and use
of watershed vegetation on streamflow, soil erosion, floods, and sedimentation.