Stand stratification and woody species diversity of a subtropical forest in limestone habitat in the northern part of Okinawa Island

Stand stratification and woody species diversity were studied in a subtropical forest in limestone habitat in the northern part of Okinawa Island, Japan. The forest stand consisted of four architectural layers. Cinnamomum japonicum Sieb. was the most dominant species as it had the highest importance value in all layers, especially in the lower three layers. Although Rhus succedanea L. was a major top-layer species, it might disappear because of its absence in the lower two layers. The lower two layers had similar floristic composition, while the composition of the top layer differed greatly from that of the lower two layers. The value of H' in each layer increased from the bottom to the second layer and then decreased, and the value of J' in each layer consistently increased from the bottom layer upward. The values of Shannon's index H' and Pielou's index J' were 4.27 bit and 0.74, respectively, at the stand level. The trends of H' and J' based on the cumulative height range from the top layer downward were, respectively, the same as those in each layer for the present forest in limestone habitat. However, these trends were opposite from those of a nearby subtropical forest in silicate habitat, where the values of H' and J' based on the cumulative height range decreased steadily from the bottom layer upward.