Effect of gap liberation on the performance and growth of dipterocarp trees in a logged-over rainforest

Abstract

Large parts of southeast Asian dipterocarp rainforests have been overlogged by applying different systems of selective cutting. Logged-over forests are expected to re-establish the original dipterocarp stock through natural regeneration. Post-logging silvicultural operations, notably crown liberation and enrichment planting, are conducted to ensure sustained yield. These techniques have largely failed to achieve the desired goal. We tested the effect of gap liberation on the performance and growth of dipterocarp trees in an overlogged concession area in south Kalimantan, Indonesia. Twelve gaps, 500–1600 m 2 in size, were sampled based on the occurrence of ephemeral dipterocarp seedling stock (notably Shorea spp.) under the canopy. Six gaps were opened up 6 years after the logging and inventoried, together with the untreated gaps, 12 years after the logging. In liberated gaps, dipterocarps accounted for 77% of the total basal area, compared with 20% in the untreated area. Survival of dipterocarps was 33% higher and diameter twice as high in liberated gaps as in the untreated plots. In height, no significant difference was detected. Liberation also improved the quality of dipterocarp trees in terms of stem and crown form. The volume of red meranti ( Shorea spp.) in liberated gaps was 90 m 3 compared with 36 m 3 in the untreated area. Gap liberation was proved as a silviculturally and economically feasible management alternative of overlogged dipterocarp rainforests.