Additivity of volume components of tree stem

Abstract

The stem volume without bark and the volume of the bark are components of the total stem volume. Therefore, an essential feature of equations of components is that they are additive, that is, that the compatibility of their estimates occurs between the components involved with their total. In this manuscript, two procedures were compared for modeling the total volume, stem volume without bark and bark volume. The first procedure (traditional) was to fit the equations of components of the volume and its total independently and the second to fit the three models by means of a system of equations. The modeling was performed from volume data of the black-wattle species (Acacia mearnsii De Wild.) using a set of forty trees. The second procedure, fitted by Weighted Nonlinear Seemingly Unrelated Regressions-WNSUR method, ensured that the volume estimates from non-linear equations of the stem components were compatibility with those the non-linear regressions for the total and with smaller variance, which makes it more appropriate method than the first one.