A comparison of transpiration rates from three semi-arid tree species in response to partial stand clearing

Rechner, Austin Francis
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As precipitation and temperature patterns continue to shift in response to climate change, total water availability including soil and surface waters are likewise altered. In central and west Texas, a common land management practice thought to increase surface water quantities and spring flow is the removal of Juniperus ashei commonly referred to as ashe juniper or cedar. Vegetative cover impacts the local water cycle through multiple feedback mechanisms including extraction of soil water by roots, and transpiration of water vapor back into the atmosphere. Through transpiration, plants exchange water for carbon from the atmosphere. This study aims to determine changes in transpiration rates pre- and post partial removal of ashe juniper (J. ashei) in a semi-arid forest located near Rocksprings, Texas using micrometeorological and sap flux data. We compared transpiration rates between three tree species - pinyon pine (Pinus remota), lacey oak (Quercus laceyi), and ashe juniper (J. ashei) under a variety of environmental conditions. Sap flow data revealed that ashe juniper used less water per day than the pines but more than the oaks. Transpiration rates increased after juniper removal with pines still transpiring the most water followed by juniper, and oaks using the least. Additionaly, it was found that pine trees located at lower elevations transpired more than individuals at higher elevations. By contrast, oak and juniper trees showed higher transpirations rates at higher elevations. An enhanced understanding of vegetation-climate interactions will provide key information for land management best practices to ensure resource resilience in the face of changing climate.