Maximising growth and sawlog production from Acacia hybrid plantations in Vietnam

Management options to optimise sawlog production from Acacia hybrid (A. mangium × A. auriculiformis) combining thinning and fertiliser treatments were applied at six sites of varying resource availability across Vietnam. Stockings at planting varying from 2000 to 1111 trees ha^-1 were thinned from 1333 to 450 trees ha^-1 (representing 27-54% thinning %) at ages 2.0-5.6 years. Tree diameter (DBH) responses to thinning were greater in the south than in the north and south central regions. Application of fertiliser at thinning increased DBH and stand volume (SV), compared with the unfertilised treatment, regardless of thinning treatment. Early thinning (at age 2-3.6 years) to 450 or 600 trees ha^-1 resulted in the greatest DBH for all diameter classes with a greater proportion of larger diameter logs. The 3-PG process-based model was applied to predict DBH and SV for all silvicultural treatments and ages. When thinning is conducted at 2-3.6 years after planting, the modelling showed that for medium and large-diameter sawlogs, the optimum rotation length is at least 5-7 years in the south and south central coast and 6-10 years in northern Vietnam.