Reduced-impact logging in Indonesian Borneo: some results confirming the need for new silvicultural prescriptions
Introduction
In the Indonesian selective logging and planting system (TPTI), all dipterocarps (i.e. timber trees in the family Dipterocarpaceae) with a diameter at 1.3 m (height dbh) over 50 or 60 cm (depending on the type of forest) can be harvested with a polycyclic felling schedule of 35 years. One year prior to harvest, forest concessionaires must carry out an inventory to determine the annual allowable cutting granted by the Department of Forestry. However, in practice these inventories are generally too inaccurate to define a satisfactory harvesting plan. In the highly productive dipterocarp forests of Borneo, where harvesting intensities commonly exceed 100 m3 ha−1 and more than 10 trees/ha, conventional logging generally damages more than 50% of the original stand (Nicholson, 1958, Kartawinata, 1978, Tinal and Palinewen, 1978, Abdulhadi et al., 1981, Cannon et al., 1994, Pinard and Putz, 1996, Bertault and Sist, 1997, Sist et al., 1998a). Because over-harvesting and poor operational practices are now recognised as an important cause of deforestation, ITTO member countries, including Indonesia, are being encouraged to revise practices in order to achieve sustainable management of the estate forests. In this context, reduced-impact logging (RIL) techniques are regarded as vital to reduce damage to a level that will preserve forest regeneration and integrity (Dykstra and Heinrich, 1996, Sist, 2000). Several experiments in mixed dipterocarp forests have demonstrated that RIL techniques can reduce damage by at least 30–50% compared with normal operation, also called ‘conventional logging’ (Pinard and Putz, 1996, Bertault and Sist, 1997). Most of the studies comparing damage under RIL and conventional logging have neglected the variability in natural forest and the variation in damage that this implies. The current coverage of such studies is very limited. This is important as the proportion of stems damaged is generally correlated with extraction rates (Nicholson, 1958, Bertault and Sist, 1997, Sist et al., 1998a) and possibly with other factors. Thus, it remains difficult to determine how general or local any conclusion might be. The main objective of this study is to assess how far RIL can reduce damage under varying felling intensity.
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Study site
The study area is located in the Indonesian Province of East Kalimantan (Borneo Island), in the district of Malinau (2°52′–3°14′N, 116°–116°40′E), within a 50,000 ha forest concession managed by Inhutani II, a state-owned timber company. The climate is equatorial with an annual rainfall measured at ca. 4000 mm. The monthly rainfall varies from ca. 200 to 400 mm (PT Inhutani II, 1996). The topography is deeply eroded with a dense network of steep ridges and drainage gullies. Elevations at the study
Results
The mean density and basal area of the four additional plots in the CNV blocks (243.6 trees/ha, SD=41; 30.4 m2/ha, SD=4.9) were not distinct from those of the 12 plots (230 trees/ha, SD=35.8 and 32.85 m2/ha, SD=4.7) set up before logging (t=0.57, df=14, P=0.58 for density, and t=0.87, df=14, P=0.40 for basal area). RIL (n=11) and CNV (n=12) plots showed similar tree densities and basal area (t=0.52, df=21, P=0.60 for density, and t=1.39, P=0.18, Table 3). The mean density and basal areas in each
Discussion
Reduced-impact techniques reduced the number of trees destroyed by 40% in comparison with conventional harvesting practices. However, the proportions of trees injured were similar in both techniques, affecting about 25% of the original stand. The main benefit of RIL was to reduce skidding damage from 25% of the original stand in CNV to only 9.5%. Because skidding operations are the major causes of mortality (Bertault and Sist, 1997), the low proportion of trees killed in RIL appear to result
Conclusions
In mixed dipterocarp forests of East Kalimantan, where density of harvestable trees often exceed 10 trees/ha, the minimum diameter rule results in high felling intensities with excessive damage to the remaining forest. RIL techniques, though they would appear to be a vital part of the solution, are useful only under a moderate extraction regime in which 8 trees/ha is an upper limit. Restricting felling intensity is essential in any case, both from the perspective of the growth and survival of
Acknowledgements
This study was carried out as a part of the project on Forest, Science and Sustainability: Bulungan Model Forest, PD12/97 Rev. 1(F) funded by the International Tropical Timber Organization (ITTO) and implemented by the Center for International Forestry Research (CIFOR), the Forest Research and Development Agency (FORDA) of the Ministry of Forestry of Indonesia, and Cirad-Forêt. The present RIL experiment would not have been possible without full support and cooperation of Inhutani II,
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