Research of ground resistance of trees growing on the arid land in Western Australia

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As a basic research for tree planting to prevent global warming, electric ground resistance of trees growing on arid land or similar land was measured and compared with that of wet area, Japan. The experiments were conveyed in Western Australia arid land, Sturt Meadows (STM) near Leonora located about 800km north east of Perth, and Two Rocks, Collie near the west coast. Also, measurement was done in Hawaii island consisting of lava ground for discussing the difference of the soil. Object trees measured during research periods were 8 species, 25 trees in STM, 2 species, 10 trees in Two Rocks, one species, 11 trees in Collie. The equivalent radius r_e and radius ratio r_e/r to the actual radius r of the object were used for estimating electrical root advance. Radius ratio was less than 0.5 in STM and Collie, more than 0.5 in Two Rocks and near 0.5 in Japan ; Object is Zelkova, native tree in Japan. Trees in Two Rocks were all big, and minimum value of the ratio was the largest among different areas. Except Two Rocks there were tendencies that the radius ration became smaller than that of Japan. Even in lava ground the minimum value of the ratio was below 0.5. This value was following to the arid land. The reason why trees having smaller value of the ratio than that in wet area existed in the arid land was considered as follows. There is a bark on the surface of the tree root, which keeps internal condition of living tissue isolating from external environment. This structure will make electrical resistance higher, and equivalent radius becomes smaller than that in wet area. As a result, it is important to search tree species having smaller radius ratio in view of tree planting to prevent global warming.