Modelling the bark thickness along the trunk with taper models

Taper models are used to determine the diameter along the trunk and allow to determine the tree trunk volume or volume of any part of it. The paper presents the method of determining the thickness of bark along the trunk using compatible taper models. Four taper models with different levels of complexity were analyzed based on data from 13 sample plots and 39 sample trees measured in black locust (Robinia pseudoacacia L.) stands from west Poland. For modelling the over and under bark diameter and bark thickness along the trunk seemingly unrelated regression of independent equations was applied. During the analyzes, the logical assumption that the thickness of the bark at any place on the trunk is determined in a difference of over and under bark diameter was applied. It was found that selected models fit the shape of the trunk with different accuracy. The worst results were obtained with the use of a polynomial model. The best fit for modelling bark thickness along the trunk was characterized by variable−form taper models. However, regardless of the complexity and quality of fit to the trunk shape, all analyzed models allowed determining the bark thickness along the trunk without systematic error and with practically acceptable accuracy