Reduction in the personal annual solar erythemal ultraviolet exposure provided by Australian gum trees

The fraction and the distribution of the personal daily solar erythemal UV exposure were assessed for the shade provided by Australian gum trees in each of the four seasons to allow evaluation of the reduction in the personal UV exposure in tree shade over a year. The personal annual erythemal UV exposures in the tree shade ranged from 2510 SED (standard erythema dose) for the vortical part of the ear to 8016 SED for the vertex of the head compared to 14,834 SED to a horizontal plane in full sun. The erythemal UV seasonal exposures for 15 min intervals on a horizontal plane in full sun in winter are comparable to the UV exposure to the vertex of the head in shade in autumn and spring. The UV exposure in the tree shade for summer, is approximately 20% less than the full sun exposure in autumn. The reduced personal annual erythemal UV exposures due to the tree shade provided reductions by a factor of 2 to 3 and 4 to 6 in the contribution to the risk of basal cell carcinomas and squamous cell carcinomas, respectively, compared to not employing the protection of the tree shade.