Growth of dipterocarp seedlings in artificial gaps: An experiment in a logged-over rainforest in South Kalimantan, Indonesia

Abstract

The objective of the study was to assess the feasibility of assisted natural regeneration of dipterocarp rainforest trees through gap simulation. Three hypotheses were tested: (1) opening of a gap enhances the rate of growth of dipterocarp seedlings; (2) growth of dipterocarp seedlings depends on gap size, being fastest in relatively small openings; and (3) growth of dipterocarp seedlings depends on gap size independently of the species concerned. Five gaps ranging from 406 m 2 to 1242 m 2 were opened up randomly in a logged-over dipterocarp forest in South Kalimantan, Indonesia, in October 1987. The measurements were carried out in October 1993, 6 years after gap establishment. A systematic line sampling survey in the surrounding forest was carried out in June 1994. Height and diameter at breast height were measured from all trees greater than 5 cm in diameter. On the basis of hypothesis testing it was concluded: (1) Diameter frequency distributions of gaps differed significantly from those of the surrounding forest area indicating that dipterocarps commence fast growth after the opening up of the gap. (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 negatively correlated to gap area. The results suggest that the optimal light conditions for fastest early growth of dipterocarps can be achieved by opening up gaps of less than 500 m 2 in logged-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 reduce the need for unnecessary treatment of the forest between gaps and thereby sustain the natural mosaic structure of the forests.