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Feel like you're baking when working around parking lots? Researchers at Arizona State University proved that not only are you baking, but the trees in the islands are baking, too. By installing a series of dataloggers under the asphalt in a commercial parking lot (some located next to landscape medians, others farther into the asphalt parking lot), researchers were able to measure not only the air temperature surrounding the parking lot, but also the soil temperature adjacent to and under the asphalt. They found that on a typical June day, with air temperature at 105°F, the surface temperature of asphalt may reach 139°F and the temperature of the rhizosphere (under the asphalt) can exceed 105°F. Earlier research shows that a 105° root zone can cause direct injury to root tissue. In addition, because of the asphalt pattern of heat conduction, maximum rhizosphere temperature occurs approximately eight hours after maximum air temperature. From a plant point of view, the shoots are stressed all afternoon and the roots are stressed well into the night. In contrast, soil temperature under turfgrass could be as much as 29°F lower than under asphalt, with very little fluctuation, providing a more favorable environment for root growth.

Source: Journal of Arboriculture, Vol. 30, No. 4, July 2004.

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