Grazing in Relation to Runoff and Erosion on Some Chaparral Watersheds of Central Arizona

Chaparral lands of central Arizona are important for water production. They are also used as grazing lands for livestock and as habitat for wildlife. An understanding of the relation of grazing to runoff and erosion is thus essential to the development of management systems for sustained high yields. This paper reports the effects of grazing on runoff and erosion as determined on four experimental watersheds called Natural Drainages A, B, C, and D. These watersheds were located on the Sierra Ancha Experimental Forest about 40 miles north of Globe, Arizona. Previous studies in the Southern Rockies suggest that grazing heavy enough to reduce the perennial grass cover results in decreased infiltration, increased surface flow of water, and additional erosion. For example, on the Rio Grande watershed, destruction of, and change in, plant cover from improper grazing was found to increase flash floods during the summer rainy season, which resulted in destructive erosion and silting of channels, reservoirs, and irrigation works (Cooperrider and Hendricks, 1937). Similar conclusions were reached with regard to improper grazing of watersheds along the Little Colorado River in northeastern Arizona (Thornthwaite et al., 1942). More recent and detailed studies suggest how grazing of a