Effect of removal of Juniperus ashei on evapotranspiration and runoff in the Seco Creek watershed

The water balance of a watershed may be affected by replacing deep-rooted woody species with shallow-rooted herbaceous vegetation. The objective of this study was to measure the effect of removing an individual species of tree, Juniperus ashei (Bucch.), on the runoff (RO) and evapotranspiration (ET) from two adjacent, unreplicated 15-ha areas (termed untreated and treated) in northeast Uvalde County, Texas, U.S.A. Daily ET from the two areas, measured from 1991 through 1995 using the Bowen ratio-energy balance method, varied from near 0 to 6 mm/d. All J. ashei taller than 0.5 m were cut with a chain saw in the treated area in September 1992. During both the pretreatment period (prior to September 1992) and the posttreatment period, the slope of treated ET as a function of untreated ET was similar to 1, suggesting that for the entire period of measurements, brush removal had no significant effect on ET. Average daily :ET from the area to be treated was 0.05 mm/d lower than that from the untreated area during the 2-year pretreatment period, while it was 0.12 mm/d lower during the 3-year posttreatment period. The ET difference (untreated minus treated:) was 0.3 mm/d in the first 2 years following removal of J. ashei and decreased thereafter. Removal of J. ashei had no consistent effect on RO. Vegetation management increased the potential for greater water yields in the short term from these rangelands by decreasing ET for the first 2 years after imposition of treatment.