GAP CHARACTERISTICS AND GAP REGENERATION IN PRIMARY EVERGREEN BROAD-LEAVED FOREST OF WESTERN JAPAN

Gap characteristics and regeneration in gaps were studied in some primary evergreen broad-leaved forests of the warm temperate zone in western Japan. Total observed 161 gaps covered 15.7% of the total land area of 8.23 ha. Gap density was 19. 6 gaps ha-1 and mean gap size was 80.3 m2. Smaller gaps (< 80 m2) were much more frequent than larger ones, and gaps larger than 400 m2 were rare. Gaps created by the death or the injury of single trees were 79.5%. Canopy trees died most often with broken trunks and not so often by uprooting or leaving standing-dead. Different types of gap regeneration behaviour were recognized among the major canopy tree species, though gap regeneration of the common evergreen broad-leaved tree species did not clearly depend on a species-specific gap size. Distylium racemosum, which occurred in equal importance (about 25%) in the canopy layer of each study stand, regenerates in gaps from saplings recruited before gap creation and can replace not only its own gaps but also gaps of other species. Therefore, it can be considered a typical climax species in this forest type of western Japan. Persea thunbergii, which can reproduce vegetatively, showed a similar type of gap regeneration behaviour. Castanopsis cuspidata can replace itself with relatively higher frequency by means of vegetative reproduction (stump sprouting) after gap creation. Quercus acuta and Quercus salicina did not regenerate under the current gap-disturbance regime. Though the frequency of uprooting is low, soil disturbance by uprooting seems to be important for the perpetuation of the pioneer tree species, Fagara ailanthoides, which recruits from buried seeds in the soil.