The Relationship between Breast Height Form Factor and Form Quotient of Liquidambar formosana in the Eastern Part of Taiwan

Abstract

The breast height form factor and quotient of trees are important parameters for calculating the stumpage volume in forest management. However, many types of datasets can only be accumulated by cutting down many trees. This research studied different thinning intensities of Formosan sweet gum (Liquidambar formosana) in the Danongdafu Forest Park, Guangfu Township, Hualien County, Taiwan. The relationship and transformation modes of the breast height form factor (F1.3) and the normal form quotient (Qn) were examined using a nondestructive terrestrial laser scanning (TLS) system, which can replace the conventional method of obtaining F1.3. The results demonstrated that the average F1.3 and Qn in the low-intensity thinning area were 0.40 and 0.56, respectively. The average F1.3 and Qn in the high-intensity thinning area were 0.48 and 0.68, respectively. Whether the stand density was low- or high-intensity could be determined statistically depending on the optimal results of F1.3. There was one mode of estimation when the stand density was 1200 trees ha−1 and another when it was 600 trees ha−1. The root mean square error of the equations used was 0.002, and the mean absolute error was <0.02. The mean percentage error was ±2.3%, and the mean absolute percentage error was <5%. If the TLS system can obtain datasets of quotient and height with surveys in the future, this would enable the calculation of F1.3. The stock volume would be calculated precisely, and the calculation error would be improved.