Towards sustainable management of tropical forest : Moving beyond RIL and minimum diameter cutting limits

The conservation potential of managed production tropical forests has helped spur the development and implementation of timber harvesting practices generally referred to as 'low-impact' or 'reducedimpact' logging (RIL). These techniques are now widely recognised as an essential component of sustainable timber harvesting prescriptions. Numerous studies in the three major tropical forest biomes (Latin America, Central Africa, South East Asia) have demonstrated that, under moderate logging intensity, these techniques can reduce by 50% the damage on residual stand and soil. However, RIL operations are still based, as all other selective logging systems operated in the tropics, on a very simple rule: the minimum diameter limit (MDCL) applied to all commercial species. In very highly stocked forests such as mixed dipterocarp forests of SE Asia, this MDCL rule leads to high felling intensities (10-15 trees/ha). Field experiments carried out by CiradForêt from 1989 to 1996 and by CIFOR since 1997 in East Kalimantan showed that under such high felling intensities, logging damage rate by RIL and unplanned logging are comparable (> 50% of the remaining tree population). The long-term consequence of such high damage rates is an increase of the rotation cycle (> 80 years) for recovery, and important changes in species density, structure and composition. As such, a minimum diameter cutting limit approach only is seldom compatible with sustainable forest management. This paper presents how RIL techniques could be improved by applying simple complementary rules. These are: (1) integration of reduced-impact logging practices into normal management operations; (2) limiting the cut to 8 or less trees/ha (with a felling cycle of 40 to 60 years to be determined according to local conditions); (3) defining minimum diameter cutting limits according to the structure, density and diameter at reproduction of target species; (4) avoiding harvesting species with less than I adult tree/ha (dbh = 50 cm over an area of 50-100 ha); (5) minimizing the size and connectivity of gaps (<600 in 2 to the extent possible); (6) refraining from postlogging treatments such as understorey clearing; and, (7) providing explicit protection for key forest species and the ecological processes they sustain. The need to prescribe complementary rules to RIL in the context of the Amazonian is then discussed. (Résumé d'auteur