Aboveground biomass partitioning and additive models for Combretum glutinosum and Terminalia laxiflora in West Africa

Accurate estimates of aboveground biomass (AGB) strongly depend on the suitability and precision of allometric models. Although additive allometric equations are expected to reduce uncertainties due to additivity property between biomass of tree components, methods for developing biomass equations do not comply with the additivity property. This study aimed to evaluate biomass allocation patterns within tree components, and to develop additive allometric equations for Combretum glutinosum and Terminalia laxiflora in West Africa. Sixty trees were destructively sampled and measured for stem, branch and leaf biomass in Sudanian savannas of Burkina Faso. Biomass allocation to stem, branch and leaf was assessed by calculating the biomass fractions for each component. Bivariate relationships between biomass fraction and diameter at beast height (dbh) were further examined. For each biomass component we tested three non-linear allometric equations based on dbh alone, and dbh in combination with height and/or crown diameter as independent variables. Seemingly Unrelated Regressions were used to fit a system of additive biomass allometric equations. Branch biomass accounted for between 60 and 70% of the AGB. Branch mass fraction increased with increasing stem diameter while a reverse trend was observed for leaf and stem mass fractions. The decline in the mass fraction was more pronounced for the leaf than the stem. Additive biomass models developed for the two species exhibited good model fit and performance, with explained variance of 68–89%. The models developed in this study provide a robust estimation of tree biomass components and can be used in Sudanian savannas of West Africa.