Reduced-impact logging in Indonesian Borneo: some results confirming the need for new silvicultural prescriptions

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Reduced-impact logging (RIL) and conventional techniques (CNV) were compared in a mixed dipterocarp hill forest in East Kalimantan in three blocks of about 100 ha each. Damage was evaluated using pre- and post-harvesting assessments in 24 one-hectare sample plots. RIL techniques nearly halved the number of trees destroyed (36 vs 60 trees/ha). RIL's main benefit was in the reduction of skidding damage (9,5% of the original tree population in RIL vs 25% in CNV). Before logging, mean canopy openness in CNV (three plots only) and RIL (9 plots) was similar. After logging, the mean canopy openness was 19.2% in CNV and 13.3% in RIL, and he distribution of the canopy class in RIL and CNV significantly different. CNV plots showed a higher proportion of measurements in the most open class than in RIL In mixed dipterocarp forest where harvestable timber density generally exceeds 10 trees/ha, a minimum diameter felling limit is clearly insufficient to keep extraction rates below 8 trees/ha. Based on these new results and previous studies in Borneo, the authors suggest three silvicultural rules: (1) to keep a minimum distance between stumps of ca. 40 m, (2) to ensure only single tree gaps using directional felling, (3) to harvest only stems with 60-100 cm dbh. Foresters, policy makers and certifiers should consider these as criteria for sustainable forest management.

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