Tree Diameter Distribution of Stands and Each Species in Largescale Cool-temperate Forest of Kyushu, Southern Japan

To elucidate size structure of cool-temperate forests of 1-10 ha order in Kyushu, southern Japan, DBH distribution was examined on semi-logarithmic scale, with reference to spatial scale, stratification and species composition. DBH distribution for 10ha-order forest (32.1’7 ha) showed a rotated sigmoid shape with a point of inflection at mid-DBH class and was composed of rotated sigmoid, concave and straight-shape distributions for older stands of 1 ha-order. DBH distribution for stratification layer in 1 ha-order stands showed straight at understory and decreasing shape at mid- and overstory. And also, the size variation increased and the skewness decreased with upper stratification layer. In terms of tall tree species within 10 ha-order forest, the degree to which the DBH distribution show decreasing to rotated sigmoid shape was roughly related to the shade tolerance characteristics of each species. On the other hand, the shape of DBH distribution for low and small-tall tree species was thought to reflect not only the shade tolerance but also the sprouting characteristics