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

Reduced-impact logging (RIL) and conventional techniques (CNV) were compared in a mixed dipterocarp hill forest in Malinau, East Kalimantan. 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 (3.6 and 3.1%) and not significantly different. After logging, the mean canopy openness was significantly higher in CNV with 19.2% than in RIL 13.3%. At a larger scale, the area of skidtrail per unit timber volume extracted was halved in the RIL compartment (15 m2 vs. 27 m2 m-3 for CNV). However, under high felling intensities (>8 trees/ha), both stand damage and canopy disturbance in RIL approached those recorded in CNV. Over this eight tree-felling threshold the effectiveness of RIL in reducing tree damage is limited. In mixed dipterocarp forest where harvestable timber density generally exceeds 10 trees/ha, a minimum diameter-felling limit is insufficient to keep extraction rates below 8 trees/ha. Based on these new results and previous studies in Borneo, we suggest three new 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.