Analysis of individual tree volume equations for Cupressus lusitanica in Munessa forest, Ethiopia

Abstract

Three different volume equations were fitted to individual tree volume (V) data collected on 260 Cupressus lusitanica trees from 49 plantations in Munessa Shashemene Forest, Ethiopia. The data were first split randomly into equation development and equation testing data sets of equal size. Diameter at breast height (D) and height above the stump to the tree tip (H) were used as independent variables to predict volume over bark from a stump height of 30cm to the tip of the tree. The parameters, standard errors and mean square errors for each of the three equations were estimated with weighted least squares regression analysis using the modelling data set. The equations were then compared on the basis of fit statistics using the equation testing data set. The equation form V = β₀ + β₁ (H/D)^β2D²H+ ε_I was the best and, therefore, it was fitted to the combined data set.

Key Words: Weighted regression, Cupressus lusitanica, volume equations

Southern African Forestry Journal No.203 2005: 27-32