Allometric equations for predicting above-ground biomass of selected woody species to estimate carbon in East African rangelands

We developed species specific equations to predict aboveground biomass (AGB) of ten woody species in Borana rangelands of southern Ethiopia. A total of 150 plants 15 for each species were measured for biometric variables including the diameter at stump height (DSH), diameter at breast height (DBH), tree height (TH) and crown diameters were destructively harvested to obtain dry biomass. Many equations that related three biomass components: total aboveground, stem and branches to single or combination of predicator variables: DSH, DBH, TH, crown area (CA) and crown volume (CV) fit the data well to predict total AGB and by components for each of the species (adj.R2 > 0.80; P < 0.0001), but the form and variables comprising the best model varied among species. The total AGB of specifics (A. seyal, A. drepanolobium and A. etbaica and Lannea rivae) was significantly predicted from a combination of DSH, and CV and that of A.bussei species by the combination of DBH and CV, with a high adjusted coefficient of determination (adj.R2 > 0.80; P < 0.0001), whereas the combination of DBH and TH best predicted the total AGB and component biomass (stem and branch) of A. tortilis (umbrella canopy shape), with adj.R2 > 0.93; P < 0.0001. A generalized mixed-species allometric model developed from the pooled data of seven species was most accurately predicted by the combination of three predicators (DSH-TH-CA models), with adj. R2 between 0.84 and 0.90 for all AGB categories. Hence, our species-specific allometric models could be adopted for the indirect biomass estimation in semi-arid savanna ecosystem of southern Ethiopia. The mixed species allometric models will give a good opportunity when species-specific equations are not available and contribute to estimate the biomass and carbon stock in woody vegetations of East African rangelands.