Site Index Curve for Taiwania Plantations in the Liukuei Area
摘要
An effective characterization of site quality is very important in forest management. Dominant height growth is calculated as a function of tree age and site, and, therefore, the evaluation of site quality is a prerequisite to computing the stand dominant height growth. Both anamorphic curves and polymorphic curves approaches were used to develop the site index model for Taiwania plantations in the Liukuei area, and their accuracy and precision were compared. Pairs of heightage observations were obtained through a stem analysis. The results indicated that based on simultaneously considering the accuracy and precision, i.e., the mean square error (MSE), the base-agespecific site index model developed by Payandeh and Wang (1994) and modified by this study was the best at estimating the site index value for all tree ages observed. In relative terms, the mean bias was ＜3% for the chosen model in the validation dataset. While there is an advantage that the estimate and application of the base-age-invariant site index model was not affected by the baseage used, this study showed a great large loss of accuracy and precision caused by base-age-invariant models, especially for those trees younger than 11 yr. Moreover, the accuracy of the site index model varied considerably depending on the choice predictor age in estimating the site index value at the base age. This study showed the tendency that for a predictor age, the closer to the base age it was, the higher the accuracy that was obtained.