Ecological Site-Scale Hydrologic Response in a Semiarid Rangeland Watershed

Abstract

Rangelands, due to their large expanse, are responsible for processing a significant portion of freshwater in the western United States. Rangeland managers are in need of methods to quantify hydrologic processes and scientifically based decision tools to effectively manage water resources under growing populations and a changing climate. The ecological site (ES) concept provides a useful framework to study complex rangeland hydrological processes in order to parameterize these tools. Traditionally, rangeland hydrology has been studied at the plot and watershed scale. ESs are intermediate-scale land units considered to have homogeneous site characteristics, which allow for mapping the spatial variability of hydrologic processes at a higher resolution compared with a lumped watershed approach. We conducted 20 variable-intensity rainfall simulation experimental runs using the Walnut Gulch Rainfall Simulator to characterize the hydrologic response of four different ESs in the Upper Crow Creek Watershed in southeastern Wyoming. An analysis of variance test with post hoc comparisons showed that sites were significantly different in runoff-infiltration dynamics. Sites ranged from exhibiting a large runoff ratio of 0.44 to infiltrating the entire applied rainfall volume. Multiple linear regressions showed that, on average, 83% of the variability of key hydrologic variables across sites could be explained by significant relationships (P ≤ 0.05) consisting of two or three ground cover variables. Beta weights for the regression variables indicated that percent cover of lesser spikemoss (Selaginella densa Rydb.) and bare soil were typically the most influential variables. Additional site-specific characteristics explain the remaining variability. The results fromthis study directly support the concept of using ESs to assess hydrologic response of rangelands. Incorporating quantitative hydrologic datasets into ecological site descriptions and decision tools should increase their utility for the management of rangeland ecosystems. © 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved.