Managing wood production from small grower acacia hybrid plantations on eroded soils in central Vietnam

Abstract

ABSTRACTAn experiment in a second rotation acacia hybrid (Acacia mangium × A. auriculiformis) clonal plantation in central Vietnam examined factors determining total wood production and its apportionment to sawlog and pulpwood. Growth and stand characteristics were compared with those in nearby plantations owned by small growers. The experimental site was on sloping land damaged and eroded by war and previous land use. The soil was shallow, with 20–30% laterised stones by volume and had lost part of the A horizon. Mean annual increment (MAI, in standing merchantable volume over bark) of the first rotation at age 8.8 years was 17 m3 ha−1 y−1. In the second rotation at age 7.6 years it was 20 m3 ha−1 y−1. Application of P fertiliser at three rates ranging from 14 to 86 kg ha−1 increased stem diameter over the second rotation although stand volume response to P was not significant by rotation end. Potassium (14 kg ha−1) gave no growth response. Growth rate was similar under weed control by herbicide and manual means. MAI increased progressively from 16.5 m3 ha−1 y−1 at the hilltop to 25.0 m3 ha−1 y−1 at the lowest part of the experiment; slope position influenced growth more than management practices. Key soil properties, pH, N, Bray-1 P and organic C were maintained from the first to the second rotation. With simple management practices including conservation of site organic matter and early stand management, appropriate for local small growers, the second rotation yielded 46% of harvested volume as sawlogs and the balance as pulpwood. Although small growers achieved similar growth rates, their current management regime does not yield sawlogs. They can influence the log categories produced and stand value through changes to stocking rate, stand management and rotation age.