The structure of lowland rainforest after selective logging in West Kalimantan, Indonesia

Abstract

To quantify forest structure following mechanized selective logging in a dipterocarp forest in West Kalimantan, Indonesia, we compared unlogged forest and sites logged 6 months, 1 year and 8 years prior to sampling. Forty-one percent of the total area was in swamp forest, interdigitated with lowland forest. Small patches of lowland forest (15% of lowland area) and 85% of swamp forest escaped logging disturbance. The canopy of 76% of lowland forest was moderately to heavily disturbed by logging; 45% was in open gap or pioneer vegetation. There was only limited evidence of canopy development after 8 years. In lowland sites logged 6 months or 1 year before sampling, forest floor was disturbed in 16% of area by roads, tractor tracks and skid trails. Local canopy disturbance increased, but at a decreasing rate, with the amount of basal area extracted. Dipterocarp trees over 50 cm in diameter at breast height (DBH) comprised 70% of total basal area before logging. The harvest removed 62% of pre-cut dipterocarp basal area and 43% of pre-cut total basal area. Small dipterocarp trees (less than 50 cm DBH, below harvestable size) suffered high mortality due to logging, possibly limiting future wood production. Logging resulted in a complex spatial mosaic of forest types and disturbance levels, suggesting options for conservation and management. Swamp forest timber resources, unharvested by conventional mechanized logging, could potentially be hand-logged by local villagers, increasing both villagers' incomes and revenue to concessions. Patches of unlogged forest may sustain some vertebrate and tree species. The detailed analysis of forest structure in this study provides part of the essential information needed to assess sustainability of management options. For the modeling of stand development that is necessary to develop an ecologically sound management system for dipterocarp forests in Indonesia, additional data on regeneration, tree growth and survival rates are required.