Relationship between stand structure and damage rate in Japanese larch [Larix leptolepis] forests damaged by glaze

Data on the Japanese larch (Larix kaempferi Carr) forest damaged by glaze in Hidaka Hokkaido in February 2004 was analyzed to work toward developing a system that minimizes glaze damage. The distribution shape of the percentage of damaged trees in each diameter class reflects that the trees can roughly be classified into five types: (1) trees with mean diameter that were more damaged than the rest, (2) trees with smaller diameters that were more damaged than the rest, (3) trees with larger diameters that were more damaged than the rest, (4) trees with variable damage rate regardless of the diameter, and (5) trees with fixed damage rate regardless of the diameter. It was assumed that these differences in the distribution shape were related to meteorological factors such as wind and icing. A linear discriminant analysis of the light and heavy damaged stands through a stand density control diagram showed that the discriminant rate had reached 75%. To identify the region where damage reduction is expected in the stand density control diagram, the borderline between the safe and the unsafe regions was drawn using the linear discriminant function and yield index (Ry=0.9) curve. Moreover, the critical slenderness ratio curve elucidated the relationship between the average tree height and slenderness ratio obtained by logistic approximation, and we found that the critical slenderness ratio changes with every growing stage. These results suggest that thinning in proportion with initial density is important in order to reduce glaze damage in forests.