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United States Department of Agriculture

Agricultural Research Service

Title: The Understory and Overstory Partitioning of Energy and Water Fluxes in An Open Canopy, Semiarid Woodland 1434

Authors
item SCOTT, RUSSELL
item Watts, C. - IMADES
item Garatuza, J. - ITSON
item Edwards, E. - UNIVERSITY OF ARIZONA
item GOODRICH, DAVID
item Williams, D. - UNIVERSITY OF ARIZONA
item Shuttleworth, W. - UNIVERSITY OF ARIZONA

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2002
Publication Date: January 1, 2003
Citation: Scott, R.L., Watts, C., Garatuza, J., Edwards, E., Goodrich, D.C., Williams, D., Shuttleworth, W.J. 2003. The understory and overstory partitioning of energy and water fluxes in an open canopy, semiarid woodland. Agricultural and Forest Meteorology. 114:127-139.

Interpretive Summary: This paper presents work from a series of 2001 experiments that made measurements of evaporation from a riparian (i.e., near-stream) mesquite woodland. Evaporation can originate from the trees or from the woodland floor. We made measurements of evaporation above the forest and below the canopy in order to understand not only what the total evaporation from the forest as a whole is, but also from what source (tree or grass/soil) it came. Since trees located near streams often acquire their water from the water table, they rely on the same source of water that the human communities in this region use. Thus, knowing how much water these types of ecosystems use and from what source it comes is important to the proper management of the groundwater resources of the region.

Technical Abstract: Eddy flux studies have traditionally focused on total ecosystem exchanges of energy and water by making measurements in the well-mixed surface layer, but this approach does not provide information about the partitioning of the total ecosystem fluxes between overstory and understory sources and sinks. In more open canopy environments, information about partitioning of fluxes is often required in order to understand the relative importance and functioning of key ecosystem components and their response to climate forcing. In this paper, we present results from a series of experiments carried out in a riparian mesquite (Prosopis velutina) woodland. Three eddy covariance systems were deployed before, during, and after the onset of the summer rainy season to measure energy and water fluxes. One eddy covariance system was installed on a tower to measure whole ecosystem fluxes. The other two were installed at a height of 2 m: one in a relatively closed understory patch and the other in a more open understory patch. Our results indicate that the understory and overstory moisture sources were mostly decoupled. The trees apparently had access to deep moisture sources, and thus, their water use was relatively insensitive to local precipitation. In contrast, the contribution of the understory to the total ecosystem fluxes was highly variable due to the presence or absence of near-surface soil moisture.

Last Modified: 7/25/2014
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