Taper Modeling on Taiwania Plantation Trees in the Liukuei Area

Abstract

Taper is used to measure the rate of decrease in the stem diameter of a tree from the bottom upwardly. Taper equations express the expected stem diameter with or without bark, as a function of the height above ground level, total tree height, and the diameter at breast height. Five tapering modeling approaches were used to estimate the stem diameter at a given height above the stump in Taiwania plantations, and their levels of accuracy and precision were compared. The results indicated that based on 3 criteria simultaneously considered, the trigonometric taper modeling approach was the worst for describing the taper of the entire tree bole, followed by the sigmoid form approach. Three-segmented polynomials, the variable-form stem profile and the polynomial form with higher-order approaches were preferred to describe the taper of the entire stem. The mean relative biases in percentage for these models on the validation trees were all ＜4%. Along the bole, the root swell (the segment from 0.3 to 1.3m in height) was the most difficult part to predict by taper modeling. However, the precision and accuracy of the prediction of tree root swell can be significantly improved using the 3-segmented polynomials or variable-form taper models.