Defense Functions of Forest Areas and Free-standing Trees with Different Tree Species and Layered Structures against Harmful Ultraviolet Rays

Abstract

In this study, the defense functions of forests and free-standing trees against UV are evaluated from actual measurements to show the importance of taking UV into account in planting designs and utilization forms of green zones of public parks, which are a field of health enhancement for urban residents. Findings obtained through actual measurements at National Showa Kinen Park in the summer of 2004 are presented below.
(1) Tree rows aligned east and west were more effective than those aligned north and south. (2) Forests with more than two layers and high trees were effective even if densities of the standing trees were low. (3) UV-B, which is scattered to a greater extent than direct sun light, was difficult to shade; UV-A, which has more of directly reaching components than direct sun light, was easy to shade. (4) The UV-shading functions of free-standing fragrant olive (Osmanthus fragrans var. aurantiacus) and Zelkova tree (Zelkova serrata) and that of a wisteria trellis ware equivalent to those of tall evergreen forests and higher than that of "an arbor" , which is an artificial structure. (5) Free-standing, low trees of Someiyoshino cherry (Prunus yedoensis Matsumura) had a low UV-shading rate but their forests showed a markedly increased UV-shading rate.