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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5135

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Summary

Portable chamber measurements of ET helped to quantify component-scale and landscape-scale contributions to ET from bare soil and sparsely vegetated, mixed species plant communities. Measurements were collected approximately every 3 months from 2003 to 2006 at the Amargosa Desert Research Site in southern Nevada. Chamber measurements of the four primary plant species and bare soil were combined in a one-layer, multi-component canopy model to estimate (1) transpiration and evaporation components from individual plant species and bare soil, respectively, and (2) landscape-scale ET. Although chamber measurements of ET from native shrubs typically surpassed those from bare soil, soil evaporation dominated landscape-scale ET during all periods measured.

Component-scale chamber ET from vegetation typically was greater and more variable throughout a given day than that from bare soil. Variability in net radiation and other factors affecting ET were more notably reflected in 15-min chamber measurements from vegetation than from bare soil. Creosote bush typically exhibited the greatest chamber ET fluxes during summer, autumn, and winter as a result of its evergreen character and high relative-plant-crown cover. During spring when all four plant species were measured, component-scale ET fluxes from wolfberry typically were greatest as a result of its high leaf density, followed by burrobush and creosote bush.

Landscape-scale ET fluxes predominantly were controlled by bare-soil evaporation; bare soil covered 94 percent of the landscape on average. Sparsely distributed vegetation (6 percent of the landscape), in turn, caused the relative importance of creosote bush and other plant species to be substantially overwhelmed. Due to its abundance across the landscape (80 percent of vegetative cover), creosote bush accounted for about 90 percent of transpiration on average and ranged from about 50 to 100 percent of transpiration for all measurement periods. Overall, transpiration accounted for about 30 percent of ET on average and bare-soil evaporation for 70 percent.

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