Direct gradient analysis was applied to the evergreen broad-leaved forest coenocline in the Tatera Forest Reserve,Japan.10 quadrats of 0.1-0.05 ha were laid out from 140 m to 560 m above sea level at intervals of 25-70 m.Gradient analysis revealed that distributions of many species terminated or started at ca.400 m.Community similarity,calculated in Percentage Similarity (PS) and Community Coefficient (CC),changed abruptly below and above the 400 m contour,suggesting a change of vegetation structure at thisaltitude,which was also clear from population distributions. The spatial turnover rate of species along the altitudinal gradient was calculated in two ways:as the Average turnover rate along the whole range of the gradient, and as the Zone turnover rate at individual altitudes.The overall rates calculated for five categories of populations:DBH>10 cm, DBH>3 cm, all woody species, herb-layer,and total vegetation,were-0.0011 to -0.0021 for PS,and -0.0009 to -0.0019 for CC.The calculated rates(PS basis) indicate that a 95% change in species composition is reached at 1120 to 620 m altitude.Similarly,the rates -0.0009 to -O.0019(CC) correspond to 1410 -680 m.The altitudinal range expected here for a 95% change agrees with the actual elevation of forest zonation in northwestern Kyushu.The average rate of both PS and CC in the herb-layer population was 1.56 times higher than the rate in the woody species population,showing a more rapid change in herb-layer population than in the woody ones along the gradient. The Zone turnover rates were higher at the 370-440 m belt than those below and above the belt.This coincided with the interchanging pattern in population distributions and the abrupt change in similarity at about 400 m above sea level.This may be due to the change in environmental conditions such as physiography and air humidity.In the diversity measurements,the species density per 100 m^2 showed a gradual increase in the DBH>3 cm population but a constant level in the DBH>10 cm population along the whole range of the forest coenocline studied,while index values of S_(100)and Shannon\u27s H\u27 showed decreasing trends in the same gradient with a few exceptionally high and low values
