Converting Chaparral to Grass to Increase Streamflow

Abstract

Chaparral covers 4 million acres in Arizona. There is interest in determining how much these lands contribute to surface water supply, and how this contribution could be changed by conversion of chaparral cover to grass or grass forb. Results from treatment in the Whitespar watersheds are interpreted. Live oak and true mountain mahogany dominate the study area, which averages 22.7 inches of annual precipitation. Whitespar B watershed was converted to grasses in 1967, and litter was not disturbed. The 246 acre watershed produced more streamflow than the untreated, 303-acre control which tended to remain intermittent. Prior to treatment, streamflow in both watersheds was quite well synchronized. Watershed b has since had continual flow. Winter flows contribute about 77 percent of the increased streamflow volume. The degree of effect is still under study, but a new rainfall-runoff relationship for the treated watershed is necessitated.