PREDICTION EQUATIONS FOR CENTERS OF GRAVITY AND MOMENTS OF INERTIA OFLOBLOLLY-PINE STEMS

Adequate design of tree harvesting equipment requires reliable estimat es of centers of gravity and moments of inertia for full trees and tre e-length stems. Several prediction models were developed for both cent ers of gravity and moments of inertia based on the theory of geometric solids. These models were fitted to center of gravity and moment of i nertia estimates that were derived from stem dimension and weight meas urements on loblolly pine (Pinus taeda L.) trees. The models were comp ared, and the best prediction equations for center of gravity and mome nt of inertia of tree-length stems were identified. Application of sta ndard multiple regression methods resulted in a moment of inertia pred iction model with a slope parameter estimate that had a sign opposite to that indicated by a theoretical model. Ridge regression and nonline ar regression were used to fit moment of inertia prediction models hav ing coefficient signs consistent with those predicted by the theoretic al model. The parameter estimates obtained by nonlinear regression wer e selected since they conformed more closely to properties of the theo retical moment of inertia model.