Studies on the reduction of the solar radiation under the isolated trees.

Abstract

One of the most important part of trees in parks and gardens is to make comfortable shade for the visitors in summer. In the shade of the tree, heavy radiant energy is extremely reduced. In this investigation, we tried to measure the decrement of the solar radiation under the isolated trees such as Japanese Zelkova (Zelkova serrata) and Chinese Sweet (Osmanthus fragrans var. auranticus) and calculated the effect of the shade of the trees. The result is summarized as follows: 1) During the daytime (9h-16h) of on clear weather at the summer, the flexes of the solar radiation measured in the shade of the trees are almost stable, and the values of radiant energy are 3mWcm2-6mW/cm2. 2) The decrement of the flexes of the solar radiation shows the maximum value on clear, and fairly weaken on cloudy. The transmissivities of radiant energy through the canopy at 12h are about 4-5% on clear 8-13% on fine and 15-40% on cloudy. A difference of the transmissivities between both trees remarkably increases on bad weather. 3) A tree which has a large and wide canopy shows strong effect. The radiant energy is decreased in 3-4mW/cm2 by the tree. This value in summer is weaker than the flexes of average groundradiation. 4) If we indicated it by using SAT (sol-air temperature) index, the effect of trees shade registered 29.8°C lower in the shade than out.