ARS | Publication request: QUANTIFYING UNDERSTORY TRANSPIRATION IN A SEMIARID RIPARIAN AREA 1792

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 2005
Publication Date: December 5, 2005
Citation: Mcguire, R.R., Scott, R.L. 2005. Quantifying understory transpiration in a semiarid riparian area. {abstract}. Eos. Trans. AGU, 86(52), Fall Meet. Suppl. Abstract H53E-0520.

Technical Abstract: One of the most challenging components to estimate when determining water budgets in semiarid basins is riparian evapotranspiration (ET). Much research has been conducted upon riparian overstory vegetation in these areas; however understory vegetation water use has been ignored due to measurement difficulties and the belief that its quantity is negligible. To better understand the magnitude of understory water use in a semiarid riparian ecosystem, we measured whole plant transpiration of the dominant understory shrub, seep willow (Baccharis salicifolia), along a perennial reach of the San Pedro River in southeastern Arizona. . Shrub transpiration was monitored using the heat balance sap flow technique and was compared under two environmental conditions: a shrub patch located in a more open environment with decreased overstory canopy cover, and a more closed shrub patch situated more directly underneath a cottonwood (Populus fremontii) forest canopy. Despite the differences in atmospheric forcing, stand-level transpiration at both sites was similar and indicated that transpiration was rarely demand-limited. Growing season transpiration totals for seep willow were much greater than precipitation and of comparable magnitude to the overstory cottonwood transpiration. These results suggest that understory water use can be an important component of a riparian water budget, especially in regions like the western U.S. where evaporative demand is often high.