GROWTH OF DIPTEROCARP SEEDLINGS IN ARTIFICIAL GAPS - AN EXPERIMENT INA LOGGED-OVER RAIN-FOREST IN SOUTH KALIMANTAN, INDONESIA

The objective of the study was to assess the feasibility of assisted n atural regeneration of dipterocarp rainforest trees through gap simula tion. Three hypotheses were tested: (1) opening of a gap enhances the rate of growth of dipterocarp seedlings; (2) growth of dipterocarp see dlings depends on gap size, being fastest in relatively small openings ; and (3) growth of dipterocarp seedlings depends on gap size independ ently of the species concerned. Five gaps ranging from 406 m(2) to 124 2 m(2) were opened up randomly in a fogged-over dipterocarp forest in South Kalimantan, Indonesia, in October 1987. The measurements were ca rried out in October 1993, 6 years after gap establishment. A systemat ic line sampling survey in the surrounding forest was carried out in J une 1994. Height and diameter at breast height were measured from all trees greater than 5 cm in diameter. On the basis of hypothesis testin g it was concluded: (1) Diameter frequency distributions of gaps diffe red significantly from those of the surrounding forest area indicating that dipterocarps commence fast growth after the opening up of the ga p. (2) Optimal gap size was under 500 m(2). (3) Shorea parvifolia grew faster than S. fallax in gaps, and the growth in both species was neg atively correlated to gap area. The results suggest that the optimal l ight conditions for fastest early growth of dipterocarps can be achiev ed by opening up gaps of less than 500 m(2) in fogged-over forests. If such gaps are opened up in places with an abundant ephemeral seedling stock of dipterocarps, this will allow more concentrated and, hence, cost-effective silvicultural operations. Gap simulation will also redu ce the need for unnecessary treatment of the forest between gaps and t hereby sustain the natural mosaic structure of the forests.