Dynamics of Primary and Secondary Warm-temperate Rain Forests in Yakushima Island

We describe the structural and dynamic feature of warm-temperate rain forests in foothill and lower montane zones of Yakushima Island, with particular reference to their potential of selfrestoration. Forest-canopy dominant is Distylium racemosum of Hamamelidaceae. Codominant species belong to Fagaceae, Lauraceae, Symplocaceae, and Theaceae. Typical primary forest stand is characterized by high biomass stock (ca. 300 t/ha) relative to short canopy stature (ca. 20 m). Though the forest is repeatedly disturbed by typhoons, the gap-area ratio in primary stands is less than 10%. Mortality amounted ca. 0.02 per year suggesting 50-year turnover of trees. On the basis of dynamic data from permanent plots for more than 10 years (mortality, recruitment rate and size growth rate), observed size structure was sufficiently reconstructed as a steady state. Allometric and architectural differentiations among the 14 abundant species are changed along their life history. Secondary stands of warmtemperate rain forest are distributed near inhabited land. Majorities of secondary stand trees are coppiceorigin primary stand species, while accompanied by deciduous pioneer trees. Tree growth rate of secondary stands is so high that the biomass-level recovery to the primary-stand state takes only 50 years after clear felling. Quick recovery of stands after clear-felling is also owing to the diversified traits among component tree species.