Abstract: Water Use by Tamarix in the Lower Colorado River System

We have been studying evapotranspiration from a variety of scales (leaf-level, canopy sap flux, tower measurements, and remote sensing) for the past decade along the Lower Colorado River and its primary tributaries. This region is located within the Mojave Desert, and experiences among the highest potential ET rates in the U.S. Leaf-level gas exchange and sap flow rates indicate that Tamarix exhibits similar water loss rates as do sympatric native phreatophytes such as willow and mesquite. However, sap flow rates in Tamarix are often higher per unit sapwood area, suggesting that dense Tamarix stands exhibit high ET rates due to the maintenance of extremely high leaf areas. We thus examined canopy water loss via sap flow in dense vs. open Tamarix stands in the Virgin River watershed of southern Nevada. We found open stands to have higher sap flow rates per unit leaf area, but dense stands have significantly higher ET rates per unit land surface area. Therefore, management programs aimed at limiting ET losses should prevent dense saltcedar stands from forming. Remote sensing studies along the Virgin River have confirmed that ET losses from saltcedar stands is highly variable along both spatial and temporal scales. We have observed vastly different ET rates in wet vs. dry years, and on a spatial scale as stream flows and depth to groundwater change along a watershed. Therefore, the notion that Tamarix stands always exhibit ET close to potential rates is incorrect, at least in the hot, dry watersheds along the Colorado River drainage.

Biographical Sketch for Stanley D. Smith

Current Position:
Professor of Biology University of Nevada, Las Vegas

Education:
B.S., New Mexico State University (1973)
M.S., New Mexico State University (1975)
Ph.D., Arizona State University (1981)
Post-Doc, UCLA (1981-1983)

Primary Interests:
Physiological Ecology of Desert Plants
Response of Desert Ecosystems to Global Change
Ecology and Water Use of Tamarix

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