Comparative studies on acorn and seedling dynamics of four Quercus species in an evergreen broad-leaved forest

The dynamics and regeneration probabilities of Quercus acuta, Q. gilva, Q. salicina, and Q. sessilifolia were studied in a 0.48 ha plot in an old-growth evergreen broad-leaved forest, Kagoshima prefecture, southwestern Japan. The canopy was well closed and had only one small gap. Seventeen tree species occurred in the canopy. The four Quercus species ranked second to fifth in basal area. Excluding the trees originated from sprouts, Q. acuta and Q. gilva lacked trees at the subcanopy layer, and Q. salicina and Q. sessilifolia had some trees at the same layer. For each Quercus species, the amount of fallen acorns fluctuated from year to year. The number of current year seedlings was positively correlated with the number of fallen acorns in the previous year. A disproportion between the spatial distribution of fallen acorns and that of established seedlings has been shown. The establishment of seedlings was frequently observed where no acorns had fallen in the previous year. Saplings of four species survived for several years and formed sapling banks under the closed canopy. During the three years of the study, the mortality of Q. salicina and Q. sessilifolia saplings was lower than that of Q. acuta and Q. gilva. However, the differences in the average annual height growth of saplings between four species were not significant, and the most of them did not grow much. These results suggest that the saplings of the four Quercus, especially Q. gilva and Q. acuta, have no chance to recruit to the canopy or subcanopy layer within a closed stand, and that some changes in the environment caused by gap formation are required for their recruitment