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

Abstract

AO_SCPLOWBSTRACTC_SCPLOWAcacia mangium Willd. is one of the most widely planted fast-growing tropical species, yet it remains poorly documented in Central Africa, particularly in terms of biomass accumulation. This knowledge gap, combined with the lack of robust allometric equations, limits the development of reliable Measurement, Reporting, and Verification (MRV) protocols for plantations. Since accurate estimates of tree volume and aboveground biomass (AGB) are essential for carbon stock assessment and for implementing climate change mitigation strategies such as REDD+, this study developed allometric equations for tree volume and AGB in A. mangium plantations on the Bateke Plateau, Republic of Congo, using destructive sampling of 54 trees (4-24 cm DBH; 25, 42, and 66 months old). Trees were measured, felled, and partitioned into trunks and large branches (>4 cm), small branches (1-4 cm), foliage, and stumps. Samples of each compartment were oven-dried and weighed. Results showed that AGB allocation to trunks and large branches increased with age, while allocation to small branches declined. A power-law model (Y = a(D2H)b) provided the best fits for both volume (Y= 0.401(D2H)0.984) and AGB (Y = 0.259(D2H)0.900). When applied to inventory data from permanent sample plots in plantations in the Bateke Plateau, estimates rose from 38.3 m3 ha-1 and 29.4 Mg ha-1 at 28 months to 157.6 m3 ha-1 and 105.5 Mg ha-1 at 64 months. These equations provide a robust reference for A. mangium in the Bateke Plateau and will strengthen the accuracy of biomass and carbon monitoring for effective forest-based climate mitigation initiatives.