Productivity of successive rotations of Acacia mangium plantations in Sumatra, Indonesia: impacts of harvest and inter-rotation site management

The impacts of wood harvest, biomass removal and inter-rotation site management practices on productivity of Acacia mangium in South Sumatra were studied over 12 years across successive rotations. The productivity measured as MAI increased from 29.4 m³ ha⁻¹ year⁻¹ in the first to 48.0 m³ ha⁻¹ year⁻¹ in the second rotation. Whole tree harvesting (total stem, branches and leaves) caused a 21 % reduction in volume compared to harvesting merchantable wood alone in the next rotation. The rates of nutrients accumulation in trees were highest during the first year of growth, and declined from age 2 years. Significant amounts of nutrients were recycled through litter fall from 1 year after planting. Results highlight the importance of management which promotes nutrient supply on stand growth. Removal of slash and litter lowered soil pH, by about 0.1 unit. A small reduction was also found in soil organic carbon and nitrogen in the top soil during the first 3–4 years but values returned to pre-harvest levels by the end of the rotation. Extractable soil phosphorus and exchangeable cations decreased by the end of second rotation but these measures underestimate the nutrient pools available for A. mangium. These findings along with results from other studies have helped to implement operations which promote conservation of site resources for sustainable production in the region.