Background: Allometric equations which are regressions linking the biomass to some independent variables that are used to estimate tree components from the forest. The generic equation developed by many authors may not adequately reveal the tree biomass in a specific region in tropics including in Ethiopia. Therefore, the use of species specific allometric equations is important to achieve higher levels of accuracy because trees of different species may differ in size and biomass. The objective of the study was to develop species-specific allometric equations for Apodytes dimidiata, Ilex mitis, Sapium ellipticum and shrubs (Galiniera saxifraga and Vernonia auriculifera) for estimating the aboveground biomass (AGB). Non-destructive sampling method was used for the measurement of tree biomass, accordingly the trees and shrubs whose Diameter at Breast Height (DBH) is ≥ 5 cm were sampled. For trees serial measurements of the height and diameter of trunk were done at 2 m intervals. For the determination of biomass of shrubs destructively sampled. Four branches were trimmed from tree and the trimmed branches were separated into leaves and wood and oven dried at 1050C and recorded to estimate the biomass of untrimmed small branches. Nested model was used and the best fit model was selected based on higher Adjusted R2, lower residual standard error and Akaike information criterion.
Results: All the necessary biomass calculations were done, and biomass equations were developed for each species. The regression equations relate AGB with DBH, height (H), and density (ρ) were computed and the models were tested for accuracy based on observed data. The best model was selected based higher adj R2 and lower residual standard error and Akaike information criterion than rejected models. The relations for all selected models are significant (p<0.000), which showed strong correlation AGB with selected dendrometric variables. Accordingly, the AGB was strongly correlated with DBH and was not signiﬁcantly correlated with wood density and height individually in Ilex mitis. In combination, AGB was strongly correlated with DBH, height and wood density; are better for carbon assessment than general equations.
Conclusions: The specific allometeric equation developed for the Gesha-Sayilem Afromontane Forest which can be used in similar moist forests in Ethiopia for the implementation of Reduced Emission from Deforestation and Degradation (REDD+) activities to benefit the local communities from carbon trade.