Soil water dynamics and water use in a western juniper (Juniperus occidentalis) woodland

This study sought to quantify changes in landscape hydrology associated with changes in juniper cover and understory vegetation. We identified rates of surface evaporation in the absence of plant cover and determined rates of soil water depletion in four cover types. Vegetation treatments were installed in a randomized block design with five replications. Additionally, juniper trees were instrumented with Granier (1985) sap flow sensors to monitor transpiration rates. At the local scale juniper removal resulted in 20% greater over-winter accumulation of soil water, and demonstrated evidence of increased; generally complementary rates of transpiration in the released understory. juniper utilizes the same resources as understory vegetation and successfully competes for shallow soil water before tapping into deeper resources. Stand-level estimates of transpiration for these woodlands averaged 0.4 mm per day during the summer months. Only 48% of the cool-season precipitation was retained in the top 90 cm in vegetated treatments but little is known about relative importance of processes governing water loss and depletion during the winter months. Resolving water use during times of low transpirational demand, will be crucial to link positive effects of juniper removal with subsurface water yield at the local scale and help further explain increased water availability observed at the watershed-scale. (C) 2013 Elsevier Ltd. All rights reserved.