VEGETATION STRUCTURE IN RELATION TO MICRO-LANDFORM IN AN EVERGREEN BROAD-LEAVED FOREST ON AMAMI-OHSHIMA ISLAND, SOUTH-WEST JAPAN

The relationship between micro-landform and vegetation structure was s tudied in a plot that was established on a slope from the ridge to the valley bottom in an evergreen broad-leaved forest on Amami Ohshima Is land, south-west Japan. Five micro-landform units recognized in the pl ot were grouped into the upper and lower slopes by their location in r elation to the erosion front, and plant distributions and vegetation s tructure were compared between them. Although small trees with d.b.h. less than 10 cm occurred almost all over the plot, the occurrence of l arger trees was limited mostly to the upper slope. Based on the spatia l distribution pattern in the plot, woody species are classified into three groups: group A mostly or strictly confined to the upper slope; group B confined to the lower slope; and group C associated statistica lly with neither slope. A well-developed forest stand, whose dominant species were Castanopsis sieboldii ssp. lutchuensis and Schima wallich ii, was seen on the upper slope, whereas only a poorly developed stand was seen on the lower slope. The difference in stability of the land surface is likely to be the major cause of the observed differences in stand structure between the upper and lower slopes. It is suggested t hat the erosion front is important as a line demarcating different hab itats within a slope from the ridge to the valley bottom.