Do trees use stemflow water? A manipulative experiment on Singleleaf piñon and Utah juniper in Great Basin woodlands.

This article investigates whether Great Basin Singleleaf piñon (Pinus monophylla) and Utah juniper (Juniperus osteosperma) trees use and benefit from stemflow, defined as precipitation routed from plant crowns down stems to soils near the plant base. Using isotopically labeled water to simulate stemflow during dry and wet years, the study found that both species took up stemflow water, with isotopic signals peaking within 2–4 days. However, stemflow constituted only about 0–2% of xylem water, and its uptake rarely alleviated plant water stress or increased sap flow, except for some water stress relief in piñon during the wetter year. The findings demonstrate rapid stemflow uptake but suggest that stemflow’s physiological benefits are limited under the tested conditions, prompting further research on its ecological role and fate in soil-plant water dynamics.