Effects of Overland Flow on Plant Water Relations, Erosion, and Soil Water Percolation on a Mojave Desert Landscape

Abstract

AbstractPrevious work in the Mojave Desert of California has shown that diversion of overland flow from alluvial piedmonts results in lower shrub density and biomass compared to that in adjacent areas that receive overland flow. In this study, measurements of predawn xylem pressure potential of creosotebush (Larrea tridentata) on three areas that were deprived of overland flow and three adjacent areas indicated that shrubs in areas of drainage‐diversion maintained higher water potentials during midsummer drought, suggesting a greater availability of soil moisture in those areas. There were no differences in the distribution of 137Cs between these areas, suggesting that drainage‐diversion has not affected erosion of surficial deposits. Mean depth of wetting of the soil profile, as indicated by the depth distribution of mobile ions (Na+, Cl−, and SO2−4) in the soil, was not significantly different between areas, although the depth to the first peak in concentration of these ions was consistently shallower in areas of drainage‐diversion, suggesting reduced percolation of soil moisture. We conclude that the higher water potential of shrubs in areas of drainage‐diversion is due to lower competitive exploitation of soil moisture than is found among the high biomass of shrubs in undisturbed areas. In contrast, soil properties have not been greatly affected by the diversion of overland flow for the past 50 yr.