Shade trees are the superstars of urban landscapes. In addition to their intrinsic aesthetic qualities, these low-tech workhorses reduce air and noise pollution, provide habitat for wildlife, increase property values, and offer cool respite for harried urbanites. Strategically planted shade trees decrease energy usage in urban buildings, absorb carbon dioxide, and supply fresh oxygen.
While studies have reported on the "cooling effect" of shade trees in temperate urban areas, similar studies for tropical or subtropical areas are limited. Climate conditions and popular tree species in the tropics or subtropics are quite different from those in more temperate regions. Now, a research team from the Department of Horticulture at National Taiwan University has published a comprehensive study in HortScience that offers recommendations for landscape designers and urban planners in subtropical regions.
Twelve species in the study provided 0.64 to 2.52ºC lower air temperature and 3.28 to 8.07ºC lower surface-soil temperature under the canopies compared with the unshaded open site. When analyzed for "cooling effect," Chinese elm (Ulmus parvifolia) and Rose wood (Pterocarpus indicus) were the determined to be the most effective, while Golden shower tree (Cassia fitula), Autumn maple (Bischofia javanica), and Swollen bamboo (Bambusa ventricosa) were the least effective. "The shading of U. parvifolia reduced air temperature by 2.52ºC but that of C. fitula only by 0.64ºC; the difference was almost fourfold," noted the authors.
http://www.sciencedaily.com/releases/2010/04/100421102453.htm
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