HYDROLOGICAL PROCESSES Hydrol. Process. 20, 3277–3288 (2006) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/hyp.6332 Springs on rangelands: runoff dynamics and influence of woody plant cover Yun Huang, 1 * Bradford P. Wilcox, 1 Libby Stern 2 and Humberto Perotto-Baldivieso 1 1 Department of Rangeland Ecology and Management, Texas A&M University, College Station, Texas 77843, USA 2 Department of Geological Sciences, University of Texas, Austin, Texas 78712, USA Abstract: To date, little effort has been devoted to understanding the nature of streamflow from dryland catchments where springs are found, and little is known about how changes in vegetation may alter that streamflow. But where they do occur in drylands, springs are important—ecologically as well as hydrologically. Areas that naturally support spring flow, such as those having an underlying karst geology, hold the most promise for increasing streamflow through control of woody plants. For rangelands, this possibility is a particularly appealing one. However, few studies have documented that such a method is effective (except in Mediterranean climates). For this reason, we studied runoff generation for a site on the Edwards Plateau of Texas: a first-order (19-ha) rangeland catchment supplied with intermittent streamflow from a spring at its base. Using hydrometric as well as isotopic characterization, we evaluated the extent to which runoff changed following removal of most of the woody plant cover (predominantly Ashe juniper). After monitoring streamflow for 4 years (two before plant removal and two following removal), we found that (1) streamflow increased following removal of juniper, by about 46 mm annually, except during the summer; (2) for the 4 years of observation, runoff made up about 22% of the water budget, with baseflow from the spring accounting for about half the total flow; and (3) hydrograph separation analysis conducted for two events following juniper removal indicated that pre-event water made up 25% and 50% of the runoff (these numbers represent lower bounds for the percentage of water derived from the spring during storm events). These findings are important, not only because they add to our understanding of runoff generation from spring-fed catchments, but also in particular because they demonstrate that where springs are present, decreasing woody plant cover may augment runoff. Copyright  2006 John Wiley & Sons, Ltd. KEY WORDS water yield; streamflow; woody plants; range hydrology; spring flow; ecohydrology; Edwards Plateau Received 1 June 2005; Accepted 20 December 2005 INTRODUCTION Springs are not a common feature on most semiarid rangelands because the soils have the capacity to store most of the water that infiltrates—the greater part of which is eventually either evaporated or transpired. However, where the soils are shallow and the underlying geology is porous or fractured, springs may develop. For example, rangelands in karst geologic settings (where underlying rocks exhibit more solution-enlarged openings than in other settings) often support springs and spring-fed rivers and streams. In these relatively dry settings, springs will supply intermittent baseflow; but during storm events, streamflow will be contributed by a larger percentage of the watershed. In many drylands where springs have existed historically, their number and output have decreased. In Texas, for example, many springs have diminished or even disappeared in the last 150 years, a period during which groundwater pumping has greatly accelerated (Brune, 2002). But woody plant cover has increased significantly during this period as well, and may also have contributed to the decline in spring flow. There *Correspondence to: Yun Huang, Department of Rangeland Ecology and Management, Texas A&M University, College Station, Texas 77843, USA. E-mail: yunh@tamu.edu Copyright  2006 John Wiley & Sons, Ltd.