We propose a method for estimating the stand density in an even-aged pure stand on a flat slope by hemispherical photography. This method is an application of the method for estimating the stand density proposed by Suzuki, i.e., distance method, and the method for estimating canopy-gap size using two photographs taken at two different heights. First, we assume a homogeneous tree height within an even-aged pure stand on a flat slope, and the straight and vertical axes of all stems. At a sample point selected from the stand randomly, two hemispherical photographs are taken with the vertically mounted camera equipped with a fish-eye lens at two different heights. Next, the radial distances between the center of the hemispherical image and the tip position of tree having the third-largest elevation angle (third-smallest zenith angle) are measured on each photograph taken at the two different heights. By substituting the measured radial distances into the relationship between radial distance and zenith angle of the fish-eye lens used, the elevation angles between camera and tip of the third-nearest tree can be obtained. Using these values of elevation angle, the distance from the photographic sample point to the third-nearest tree can be geometrically computed, and then the stand density can be estimated by substituting the computed distance into the equation of Suzuki's distance method.
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