Economic Efficiency Assessment of Acacia mangium Plantations Managed for Small-Diameter Timber and the Potential Development of Large-Diameter Timber Production Scenarios in Bac Ninh Province, Vietnam

This study evaluates the economic efficiency of Acacia mangium plantation models managed for small-diameter timber under a 6-year rotation, while also estimating the potential revenue from a large-diameter timber production scenario based on a 15-year rotation in Bac Ninh Province, Vietnam. The study draws on data from 20 sample plots and interviews with 50 forest-growing households. The methods employed include forest growing stock estimation and financial analysis using Net Present Value (NPV), Internal Rate of Return (IRR), and Benefit-Cost Ratio (BCR). The results indicate that, at 6 years of age, standing timber volume ranges from 168.13 m³/ha to 260.36 m³/ha, with the highest volume recorded at a planting density of 3,330 trees/ha. Revenue from small-diameter timber harvesting ranges from 130.133 to 185.245 million VND/ha. The highest revenue is achieved at a planting density of 3,333 trees/ha (185.245 million VND/ha), followed by densities of 2,500 trees/ha (172.852 million VND/ha) and 2,000 trees/ha (169.060 million VND/ha), while the lowest revenue is recorded at a density of 1,333 trees/ha (130.133 million VND/ha). All four models demonstrate economic viability, with NPV values greater than zero. Among them, the model with a planting density of 2,000 trees/ha delivers the highest investment efficiency, with an NPV of 60.94 million VND/ha, a BCR of 2.77, and an IRR of 39.69%. Under the large-diameter timber production scenario, the estimated revenue from the main harvest at age 15 ranges from 830.84 to 969.32 million VND/ha. This is approximately 2.24–2.62 times higher than the revenue generated by small-diameter timber model M1 and 2.46–2.87 times higher than that of model M3. Compared with small-diameter timber production over the same 15-year period, the large-diameter timber scenario offers the potential to increase revenue from the main harvest while reducing the frequency of reforestation investments. These findings provide a scientific reference for determining appropriate planting densities and guiding the transition of Acacia mangium plantation management toward greater economic value and sustainable forest management.