Abstract
Forest biomass is estimated through direct and indirect methods. The indirect method is less costly and efficient. Biomass equation is one of the indirect methods to estimate biomass using certain parameters. However, very few biomass equations have been developed for limited tree species in Ethiopia and hence, generic biomass equations are usually used. This may under or overestimate the biomass. Besides, the accuracy of biomass estimate using the different methods was inadequately studied.
Therefore, the general objective of this study was to evaluate the performance of semi-destructive and generic method in reference to destructive method for Cupressus lustanica grown at Wondo Genet, South central Ethiopia. For the semi destructive method 30 sample trees (10 from each age group) were selected from three ages (5, 12 and 24). Sample trees were measured for their biometric parameters such as diameter at breast height (DBH), diameter at stump height (DSH), and total height (H). For the sampled trees 10% of the total branch counts were trimmed for further parametric measurements. Based on the collected data 6 models were fitted using R 3.2.3 (R Development core team 2019). The best biomass equations were selected on the basis of different performance statistics (Bias, RMSE, PRESS, AIC, D and R2). The best performing total above ground biomass equation by semi-destructive method was Y = 0.07407x D1.01228 x H1.5674 (R2= 0.94 , p =3.882e-12). Estimation performance test was conducted for the semi-destructive model (this study) and generic model (Vigil, 2010) by using the destructive model (Leakemariam, et al., 2013) as a reference. Pair wise t-test was used to test the significance of the variation on above ground biomass estimation. The semi destructively developed and generic above ground biomass models underestimated by 18.7% and 39.4% respectively. The result of the pair wise t-test showed that the difference was insignificant for the semi destructive method (P=0.9059), while it was significant for the generic model (P= 0.0294) in reference to the destructive method. It was concluded that semi destructive method can estimate the above ground biomass of Cupressus lustanica as good as the destructive method. This can make the process of biomass equation development less costly and environmentally friendly.
Keywords: Biomass equations, Biomass, component biomass, Semi destructive method
