ARS | Publication request: Piñon and juniper summer water source partitioning: stemflow vs. groundwater

Submitted to: Society for Range Management
Publication Type: Abstract Only
Publication Acceptance Date: November 1, 2011
Publication Date: N/A

Technical Abstract: Piñon (Pinus monophylla) and juniper (Juniperus osteosperma) trees have been encroaching into sagebrush communities throughout the Great Basin, which has reduced the cover of sagebrush and native grasses. This has affected wildlife habitats and impacted rangeland grazing areas. Piñon-Juniper (P-J) stands alter the hydrology of these systems by intercepting rainfall and competing for limited water resources that might otherwise be available to understory plants. Research on P-J interception found approximately 10% of the water that is intercepted during simulated summer rainstorms is funneled to the base of the tree trunk via a process known as “stemflow”. We hypothesized this redistribution of rainfall into stemflow would improve the water status of P-J. The objectives of this research were to: 1) quantify how much water P-J use in summer and 2) determine if stemflow is used by P-J trees. The amount of stemflow for individual trees was determined by simulating a 19 mm rainfall on six piñons and six junipers and capturing all stemflow. After trees dried, this volume of water was then labeled with a stable isotope tracer and applied to the trees in a way that simulates stemflow. Total water use was measured with Granier sapflow probes and stable isotope methodology was used to determine plant water sources. Plant water potential was measured to determine plant stress. Data will be analyzed using a two-way repeated measures ANOVA, with species and days since stemflow irrigation as the main factors, to detect changes in stable isotopic composition of plant xylem water and water potential.