Microtopography and distribution of canopy trees in a subtropical evergreen broad-leaved forest in the northern part of Okinawa Island,Japan

The spatial distribution of trees in relation to topography was investigated using two topographic indices, slope steepness and slope configuration, in a 4-ha plot in a subtropical evergreen forest in the northern part of Okinawa Island, Japan. Most species showed an aggregated distribution and patch size was related to various microtopographical features, including small ridges and valleys. In a cluster analysis based on the dissimilarity of each species distribution, the species were divided into three major clusters. A significant correlation between the dissimilarity and the distance between each species on the axis of the two topographic indices indicated that species association was, in part, explained by the topographic indices. I suggest that species distributed on steep and concave slopes regenerate depending on disturbances such as landslides on unstable topography, whereas species distributed on ridges and upper slopes regenerate depending on the canopy gap. A number of species that were less abundant in the 4-ha plot occurred in the riparian area near a stream, where the density of more abundant species was low. The results of this study support the existence of habitat niche divergence related to topography in a subtropical evergreen broad-leaved forest.