Allometric equations for estimating biomass in agricultural landscapes: I. Aboveground biomass

Meeting the reducing emissions from deforestation and degradation (REDD) framework demands stringent carbon measuring, reporting and verifying methods. In most cases, estimates of aboveground carbon stocks rely on allometric equations. Although generic and species-specific allometries have been developed for conventional areas such as forests, their use in agricultural landscapes is questionable as agricultural trees are typically managed and rarely mono-specific. Therefore, there is a need to develop a robust generic allometry that accounts for the heterogeneity of tree diversity throughout the landscape. Allometric equations were developed from empirical destructive sampling of 72 trees (diameter at breast height (dbh): 3–102 cm) from three 100 km2 benchmark sites in Western Kenya. Diameter at breast height alone provided reliable prediction for aboveground biomass (17 ± 0.02 Mg C ha−1) with >95% accuracy. Published equations overestimated landscape biomass due to errors in either smaller trees (dbh <10 cm) which dominate the landscape (66%) or the few larger trees (dbh >40 cm) which constitute 3% of all the trees but hold most of the biomass (48%). The apparently small differences in the equations for small trees could add up to a large amount of carbon when looking at a landscape. This study recommends diameter as the basis for assessing tree biomass in Western Kenyan agricultural mosaics. The equations developed are a useful tool for assessing the potential for carbon sequestration in agricultural landscapes and represent key information for scaling biomass estimates for entire landscapes.