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United States Department of Agriculture

Agricultural Research Service

Research Project: ENHANCING ENVIRONMENTAL QUALITY AND ECOSYSTEM SERVICES IN SOUTHEASTERN U.S. COASTAL PLAIN AGRICULTURAL WATERSHEDS

Location: Southeast Watershed Research

Title: Forest transpiration from sap flux density measurements in a Southeastern Coastal Plain riparian buffer system

Authors
item Bosch, David
item Marshall, Laura -
item Teskey, Robert -

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 8, 2013
Publication Date: January 3, 2014
Citation: Bosch, D.D., Marshall, L.K., Teskey, R. 2014. Forest transpiration from sap flux density measurements in a Southeastern Coastal Plain riparian buffer system. Agricultural and Forest Meteorology. 187:72-82. http:/dx.doi.org/10.1016/j.agrformet.2013.12.002.

Interpretive Summary: Riparian forest buffers make up a large portion of the landscape in watersheds in the Southeastern Coastal Plain Region of the United States (US). Because of this and high potential water consumption, transpiration of these buffers is an important component of watershed hydrologic budgets. Sap velocity was measured within a 720 m2 riparian buffer in South-central Georgia US in order to quantify transpiration and its role in watershed hydrology. Data indicated annual transpiration of the measured area was 86% of annual precipitation. Moreover, the water consumption attributed to transpiration of the zone was disproportionate to the area occupied by the buffer, an important consideration when examining overall water consumption in regional watersheds

Technical Abstract: Forested riparian buffers are prevalent throughout the Southeastern Coastal Plain Region of the United States (US). Because they make up a significant portion of the regional landscape, transpiration within these riparian buffers is believed to have an important impact on the hydrologic budget of regional watersheds. A riparian buffer along a first order stream in South-central Georgia US was selected for a sap velocity study designed to provide measurements of tree transpiration. The forest provided a buffer zone that averaged 70 m in width from an upland field to the first order stream. Shallow water table conditions allowed direct interaction between the tree’s active root system and groundwater. Sap velocity, groundwater, and climatic data were collected to determine transpiration rates from different tree species and their relationship to potential ET rates and hydrologic and environmental conditions. Average sap flow rates ranged from 2 to 133 L day-1. Sap velocity was related to tree diameter, solar flux density, and daily vapor pressure deficit. On an area basis, the average annual transpiration for the studied 720 m2 study area was 1175 mm year-1. This represented 86% of annual precipitation and 88% of annual potential evapotranspiration (PET). While landscape position and subsequently access to groundwater did not appear to strongly influence sap velocity rates, reduced soil water in the vadose zone led to reductions in tree transpiration. The data indicate that transpiration within regional buffers uses a disproportionate amount of water on a per area basis compared to upland land covers, an important consideration when examining overall water consumption in regional watersheds.

Last Modified: 7/25/2014
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