LAUSR

Abstract Juniper expansion into sagebrush-dominated communities is a phenomenon occurring across large regions of the western U.S. in the past century. We investigated the competitive abilities for belowground resources of Juniperus osteosperma (Utah juniper) and Artemisia tridentata (big sagebrush) based on fine root traits and spatial patterns of water uptake inferred from stem and soil stable oxygen isotopes (δ18O). Data were collected from neighboring J. osteosperma and A. tridentata plants in northern Colorado and included measurements of different size classes of J. osteosperma: short ( 3 m). Short J. osteosperma switched from utilizing shallow to primarily deep water sources across the growing season. Artemisia tridentata had root traits associated with faster root proliferation and resource acquisition (significantly greater specific root length and smaller root diameter, p   .1). Additionally, we found that short J. osteosperma individuals can quickly develop deep root systems, but there is little difference in belowground foraging between individuals of J. osteosperma and A. tridentata based on the depth of water uptake and root length density.