Allometric equations for estimating tree volume and aboveground biomass of Acacia mangium Willd. on the Batéké Plateau, Republic of the Congo.

Abstract

Acacia mangium Willd. is a widely planted fast-growing tropical species, but species-specific equations for estimating its tree volume and aboveground biomass remain scarce across tropical Africa. Accurate estimation of these parameters is essential for assessing plantation resources and carbon stocks and for supporting climate-change mitigation initiatives such as Reducing Emissions from Deforestation and Forest Degradation (REDD+). This study developed allometric equations to estimate woody volume and AGB in A. mangium plantations on the Batéké Plateau (Republic of the Congo). A total of 54 trees, ranging from 4.5 to 23.8 cm in diameter, were destructively sampled. Trees were measured, felled, and partitioned into stem and large branches (>4 cm), small branches (1-4 cm), phyllodes, and stumps. Subsamples of each compartment were oven-dried and weighed. Results showed that biomass allocation to the stem and large branches increased with tree age, while allocation to small branches and phyllodes declined. A power-law model (Y = a(D²H)ᵇ) provided the best fit (low values of AIC, BIC, RMSE, and bias) for both volume (V = 0.401(D²H)0.984) and AGB (AGB = 0.259(D²H)0.900). When applied to inventory data from permanent sample plots (trees aged 28-64 months), estimates (mean ± SE) ranged from 38.29 ± 0.90 to 157.62 ± 12.30 m3 ha-1 for volume and from 29.41 ± 0.70 to 105.51 ± 8.20 Mg ha-1 for AGB. These equations provide a robust reference for A. mangium on the Batéké Plateau and will strengthen the accuracy of biomass and carbon monitoring for effective forest-based climate mitigation initiatives.