抄録
It is important to monitor the growing state of tree roots without digging the soil away from the bottom of the tree. Ground resistance of tree roots indicates the grade of the growing state. However, ground resistance of the tree is modified by resistivity of the soil. This disables the comparison of the growth level of trees in different places. In order to make the comparison possible among them without influence of soil resistivity, the value of ground resistance of the tree is converted to that of a metal disk electrode. If we know the soil resistivity, a radius of the disk becomes to be known. This disk radius is called the equivalent radius. Using the equivalent radius, we can estimate the growth level of trees growing in different places evenly. The results of field studies on some trees are shown.
