Variable-shape stem-profile predictions for western hemlock. Part I. Predictions from DBH and total height

Abstract

A system of three conditioned equations is used to describe whole-tree taper for western hemlock (Tsugaheterophylla (Raf.) Sarg.). Geometric attributes of the system are predicted as empirical functions of DBH and total height. This allows for a wide range of predicted stem profiles without risk of illogical profile predictions for any tree size. Fitting is by multivariate nonlinear regression, where the dependent variables are inside-bark diameters at 12 points on each sample tree. Residual analysis shows that the system does mimic the data in the prediction of different profiles for various combinations of DBH and height. The resultant system can produce analytically tractable estimates of volume. The goodness of fit of the compatible volume estimator is comparable with that of the best whole-tree volume equations. A product of the analysis is a multivariate description of the error distribution; this could have application in the development of profile prediction systems that utilize diameter measurements at multiple heights.