Penetration of Solar Erythemal UV Radiation in the Shade of Two Common Australian Trees

The penetration of solar erythemal ultraviolet (UV) radiation has been measured in the shade of a gum (Eucalyptus sp.) and a she oak (Casaurina) tree, both on a horizontal plane and with polysulphone dosimeters to human anatomical sites. This has provided new data useful for protection strategies against harmful UV radiation. For larger solar zenith angles, the relative penetration of solar erythemal UV in the shade of the trees is higher. On a horizontal plane, at noon, in winter, the shade erythemal UV ranged from 44 to 55% of that in the sun whereas in spring it ranged from 29 to 37% of the irradiances in the sun. Similarly, at 9:00 EST and 15:00 EST, the shade erythemal UV in winter ranged from 51 to 81% of the irradiances in the sun whereas in spring and summer they ranged from 35 to 51% of the unshaded irradiances. The shade ratios for specific body sites provided by the shade of the two trees was 0.05 to 0.45 for the solar zenith angles in this research. The shade ratios ranged from 0.14 to 0.45 for the gum tree and from 0.05 to 0.28 for the she oak. The denser foliage of the she oak provided the higher UV protection compared to that of the gum tree.