Taper is used to measure the rate of decrease in stem diameter from the bottom upwardly.
Taper equations express the expected stem diameter outside or inside the bark, as a function of the
height above ground level, total tree height, and diameter at breast height. Four tapering modeling
approaches were used to estimate the stem diameter at a given height above the stump in Calocedrus
formosana plantations and compare their accuracy and precision. The results indicated that
while there was little difference in describing the overall tapering performance, based on 3 criteria
considered simultaneously, the variable-form stem profile was the best at describing the taper of
the total tree bole, followed by 3-segmented polynomials. The mean relative biases for these models
on the fitted trees were < 6%, except for the polynomial form with a higher-order approach.
The butt swell (segment from 0.3 to 1.3 m in height) is a part of the stem that is the most difficult
to predict in tapering modeling for all models used. However, the precision and accuracy in the
prediction of the tree butt swell can be impressively improved using variable-form taper models.