Patten (.1975) obtained similar results for microenvironments beneath palo verde trees. Nighttime temperatures under collector field may not be as easy to predict due to the complication of wind deflection by arrays of collectors, and their effect on nocturnal inversions, which will be discussed later. Although early evening temperatures should be cooler under collectors (assuming cooler temperatures during the day), interception and possible reradiation of long-wave emitted radiation should retard nocturnal cooling relative to that in the open desert. ERDA (1977b) predicts no significant difference in nighttime temperatures. When comparing temperature and organism function, Terjung et al. (1970) state that total environmental radiant temperature is more important in determining organism heat gain or loss than the popularly used air temperature. Radiant temperature is the temperature that a black body would have to be at to produce thermal radiation equal to the downward counterradiation of the sky (Terjung et al. 1970) , and is calculated from the total radiation flux using the Stefan-Boltzmann equation (Schmidt- Nielson et al. 1965). Studies using this parameter have shown significant reductions in radiant temperatures in shaded desert habitats. Dawson and Denny (1969) report radiant temperatures beneath the canopies of black oak and mulga {Acacta} trees in arid Australia to be 55% and 49% of that in the open, respectively. Lowe and Hinds (1971) found palo verde trees in Arizona to reduce this parameter an average of 37% in the winter with respect to daily maximum value. Furthermore, Lowe and Hinds (1971) found winter nocturnal radiant temperatures associated with the infra-red flux to be much higher under a palo verde canopy than in the open, once again due to the canopy blocking the sky and thus limiting loss of thermal radiation from the surface. Surface and soil temperatures should be influenced far more than air temperatures due to shading. Cloudsley-Thompson (1965) and Patten and Smith (1974) observed desert surface temperatures in the shade to be similar to air temperatures, while exposed temperatures may reach 80°C (Cloudsley- Thompson 1965), with a diurnal range of up to 55°C (Geiger 1965) . Although trees and shrubs in arid regions are known to significantly reduce surface temperature in the warm season when they are fully leafed out (Shreve 1931,
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