Analysis of Standing Trees Using a Motion Capture System: A Three-Dimensional Stem Model for Basal Sweep of Japanese Cedar (Cryptomeria japonica D. Don.)

Abstract

In regions of heavy snow, Japanese cedar shows “basal sweep” due to snow pressure damage and experiences irregular growth. We reconstruct the shape of basal sweep of Japanese cedar for the first time by applying a motion capture system for three-dimensional (3D) visualization. Based on the reconstructed shape, we discuss the eccentric growth and volume variation involved in the basal sweep of Japanese cedar. The location coordinates of the basal sweep stem and ground surface were measured using a magnetic digitizer and the annual ring coordinates of the disks were converted using a translation and rotation matrix. The coordinates of the annual rings were converted into corresponding locations in the stem with a custom software program. This method afforded a view of the relationship among the annual ring width, shape of the trunk, and standing tree condition. Three patterns of eccentric radial growth were observed in the basal sweeps of young trees, and these patterns were distinct depending on the stem height. The tree volume of young trees was over 27 times that of old trees, but the basal sweep volume showed only a six-fold difference. The mean ratio of the basal sweep volume to total volume was 68.8% for young trees and 25.3% for old trees.