Developing A Form Factor Function for Acacia Decurrensin Southwestern Amhara National Regional State, Ethiopia

Volumetric estimation is very important for a sustainable management of forest resources, yield prediction and also to know its growth rates. It is the product of DBH, tree height and form factor. Acacia decurrens Willd is extensively grown as a rotational crop for charcoal and productivity improvement in woodlot of Awi Zone. The objective of the study was to develop a form factor function that can estimate the stem profile of the tree species. Pollanschutz’s, F. Evert’s, Short Swedish’s, Mayer’s and Rosset’s form factor functions were tested to select the best one. The data were collected at 58 destructed trees from five years aged in two woodlots and one community-managed plantation of A. decurrens during farmers’ harvesting. To predict the volume of the species, all the functions were evaluated by Root mean square error (RMSE), mean absolute deviation (MAD), coefficient of variance (CV) and graph behavior of observed form factor. The performance of all functions was almost similar even though we chose Mayer’s and Pollanschutz’s functions due to their relatively lower values of RMSE, MAD and the nature of the graphs of predicted versus observed form factors are nearly stable. Based on this, 0.4875 was recommended to estimate the above ground stand volume of A. decurrens with a DBH range of 8-14cm for the five years old woodlot in the study site.