Low-tech cool: Shade trees for subtropical streets

Apr 21, 2010

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. It's no coincidence that researchers around the world are working to find the best shade trees for all types of urban environments.

While studies have reported on the "cooling effect" of shade trees in temperate urban areas, similar studies for tropical or subtropical areas are limited. 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 that offers recommendations for landscape designers and urban planners in subtropical regions. Bau-Show Lin and Yann-Jou Lin evaluated the differences in cooling effect of trees and bamboo grown in Taipei, Taiwan.

The effect of shade trees on the air and surface-soil temperature reduction under the canopy was studied in a park in Taipei City, Taiwan. Ten species of trees and two species of bamboo, which had tightly clustered tall stems and spreading branches resembling trees, were chosen for the study. Microclimate conditions under the tree canopies and an unshaded open space were measured repeatedly at midday without precipitation. The researchers analyzed four characteristics of each plant related to cooling effect, determining that foliage density had the greatest contribution to cooling, followed by leaf thickness, leaf texture, and leaf color lightness. Regression analysis also revealed that , wind velocity, and vapor pressure at the site had significant effects on temperature reduction attributable to shade trees or bamboo.

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.

"This research could help maximize the cooling effect of shade trees by careful selection of species based on their canopy and leaf characteristics", the authors said. They added that although the field studies were carried out in a park, the results can be applied to shade trees in other subtropical .

Explore further: Noted researchers warn that biomedical research system in US is unsustainable

More information: The complete study and abstract are available on the ASHS HortScience electronic journal web site: hortsci.ashspublications.org/cgi/content/abstract/45/1/83

Provided by American Society for Horticultural Science

4.5 /5 (2 votes)
add to favorites email to friend print save as pdf

Related Stories

Shade Tree Coverage Reduces Power Costs

Nov 15, 2008

An Auburn University study sheds new light on just how valuable shade trees are in reducing homeowners’ electricity bills during hot summer months.

New Study: Home Energy Savings Are Made in the Shade

May 06, 2009

(PhysOrg.com) -- Trees positioned to shade the west and south sides of a house may decrease summertime electric bills by 5 percent on average, according to a recent study of California homes by researchers ...

Nurseries to Give Big-City Test to Cloned Trees

Jul 05, 2006

New York City life is tough on trees. Compacted soil with high pH, low-hanging utility wires, an environment often hot and dry, and the city's harsh winters challenge a tree's survival and colorful foliage.

Recommended for you

Plants with dormant seeds give rise to more species

7 hours ago

Seeds that sprout as soon as they're planted may be good news for a garden. But wild plants need to be more careful. In the wild, a plant whose seeds sprouted at the first warm spell or rainy day would risk disaster. More ...

Researchers successfully clone adult human stem cells

11 hours ago

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

User comments : 0

More news stories

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Plants with dormant seeds give rise to more species

Seeds that sprout as soon as they're planted may be good news for a garden. But wild plants need to be more careful. In the wild, a plant whose seeds sprouted at the first warm spell or rainy day would risk disaster. More ...

Researchers develop new model of cellular movement

(Phys.org) —Cell movement plays an important role in a host of biological functions from embryonic development to repairing wounded tissue. It also enables cancer cells to break free from their sites of ...

Male monkey filmed caring for dying mate (w/ Video)

(Phys.org) —The incident was captured by Dr Bruna Bezerra and colleagues in the Atlantic Forest in the Northeast of Brazil.  Dr Bezerra is a Research Associate at the University of Bristol and a Professor ...

Impact glass stores biodata for millions of years

(Phys.org) —Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth. Scientists ...