Weather and evapotranspiration studies in a saltcedar thicket, Arizona

Abstract

Water use by saltcedar, Tamarix chinensis, was studied from 1961 through 1967 near Buckeye, Ariz. The test site was located on the rim of the Gila River flood plain and was bordered on the north, east, and west sides by fetches of dense saltcedar thickets 1 or more kilometers wide. On the south side, however, the fetch was less than 100 meters.The climate of the area, typical of the Sonoran Desert, is characterized by low humidities, strong winds, and temperature extremes of <-lOoC in winter and >50°C in summer. Potential evaporation values are among the highest observed in the United States.Rates and quantities of evapotranspiration were observed in six plastic-lined evapotranspirometers (tanks) whose 81 square-meter surfaces were planted to saltcedar having heights and density equal to those of the surroundings.The test site was further equipped with instrumentation to measure the following data: solar short-wave radiation; long-and shortwave net radiation; albedo; humidity, temperature, and wind profiles in and over the vegetation; soil-temperature gradients and soil-heat flux; moisture content of the soil; and carbon dioxide content of the air. Detailed studies were made of the microclimate in and over a typical saltcedar thicket. Analyses showed that, above the vegetation, the wind profiles in more than 80 percent of the observations were logarithmic. Within the thickets considerable turbulence and irregular wind inversions (tunneling) occurred during daylight hours.It was concluded that transport constants for momentum, heat, and vapor are the same more than 80 percent of the time because plots of windspeed versus temperature at different heights and of windspeeds versus vapor pressure at those heights fall on straight lines. Fluxes of carbon dioxide and vapor are closely related. Vapor fluxes diminish, as do rates of photosynthesis, during hot afternoons when temperatures exceed 40°C, suggesting a variable stomatal resistance factor.Estimates of potential evapotranspiration rates using various models were plotted against measured values. For rough estimates of total yearly quantities of evapotranspiration, three independent methods gave values closest to those measured by evapotranspirometers with the shallowest (1.5 m) depth to water and with low salinity of soil moisture. (The effects of depth-to-water and of salinity have been discussed extensively in "Water use by saltcedar as measured by the water-budget method" (van Hylckama, 1974, U.S. Geological Survey Professional Paper 491-E).For short-term estimates (of the order of 1 hour) the 1966 combination method of C. H. M. van Bavel gave results that were too high during daytime hours. When appropriate corrections were made by taking stomatal and aerodynamic resistances into account, the calculated values fitted the measured ones very well. This shows that saltcedar reacts to extremely high windspeeds and temperatures by stomatal closure, thus diminishing evapotranspiration even though water is freely available (as it is in evapotranspirometers with favor...

Life on the edge – to which degree does phreatic water sustain vegetation in the periphery of the Taklamakan Desert?

“…Over centuries saltcedar forms characteristic conical hillocks, called nebkhas (Killian 1945; Long 1954; Le Houérou 1986). In the arid regions of North America, where T. ramosissima had been introduced in the early nineteenth century (Everitt 1980; Macmahon & Wagner 1985; Frasier & Johnsen 1991), the species is reported to grow at maximum groundwater depths of 7‐10 m (van Hylckama 1980; Graf 1982; Stromberg 1998), which is at considerably shallower groundwater tables than found by us (i.e. at maximum 14 m plus about additional 10 m for high dunes).…”

Open field host selection and behavior by tamarisk beetles (Diorhabda spp.) (Coleoptera: Chrysomelidae) in biological control of exotic saltcedars (Tamarix spp.) and risks to non-target athel (T. aphylla) and native Frankenia spp.

“…Exotic saltcedars (Tamarix spp., Tamaricaceae: Tamaricales, known as cedros salados in México) from Eurasia and Africa (Baum, 1978;Crins, 1989), introduced to North America for erosion control and as ornamentals in the 1800s, have come to dominate many arid riparian habitats in western North America (Robinson, 1965;Baum, 1967;Friedman et al, 2005;Birken and Cooper, 2006), causing great ecological and economic damage (DeLoach et al, 2000, in press;Zavaleta, 2000) to water and wildlife resources (van Hylckama, 1980;Gay and Hartman, 1982;Weeks et al, 1987;DeLoach and Tracy, 1997;DiTomaso, 1998;Lovich and de Gouvenain, 1998;Kennedy and Hobbie, 2004;. Saltcedar trees support reduced levels of faunal diversity compared to native vegetation (Boeer and Schmidly, 1977;Engle-Wilson and Ohmart, 1978;Kerpez and Smith, 1987;Knutson et al, 2003).…”

Ground-water and surface-water relations along the Mojave River, southern California

“…These evapotranspiration rates agree fairly well with the results of a water-budget study along the Gila River flood plain in Arizona (Culler and others, 1982) and energy-budget evapotranspiration measurements along the Pecos River flood plain in New Mexico (Weeks and others, 1987). Agreement with studies of tank-measured evapotranspiration (Gatewood and others, 1950;van Hylckama, T.E.A., 1980) is poor. As pointed out by Weeks and others (1987, p. 7 and 30), the much larger evapotranspiration rates determined from tank experiments are probably due to oases effects on the tanks, and they probably represent the maximum rates of evapotranspiration that might occur with an unlimited water supply.…”