Abstract:

【Objective】 The site index method is a common way for forest site quality evaluation, and dominant height is an important parameter in the site index model. The purpose of this study was to develop dominant height growth models for Chinese fir plantation using age-independent methods to predict dominant height growth under the scenario that sand age remains unknown. This kind of age-independent difference approach formulation is established to stimulate the growth of trees and stands. It is used to predict the growth at the end of every period by the observation at the beginning of the period.【Method】 With data of 65 permanent sample plots in Jiangle State-owned Forest farm of Fujian Province, nine age-independent models were developed respectively based on Richards, Lundqvist-Kolf and Hossfeld growth equation. Three statistics indicators including coefficient of determination(R²), mean error and root mean square error and graphical analysis were considered to evaluate models and choose the best one. This method has little application at home but it can improve the situation that ages are difficult to get or not able to attain. It can provide a new way to establish dominant height model and it will make site index evaluation become a more convenient thing.【Result】 The nine models showed robust goodness of fit, and the best one was identified as the model derived from Hossfeld function with parameter a as expand parameter of stand factors. Besides, its predictive accuracy is higher for short age intervals.【Conclusion】 Age-independent site index model can accurately fit and predict dominant height growth, it is accurate and effective for site index model derivation, so it is recommended that age-independent site index model should be used to estimate site quality for uneven-aged stands or age unknown situations.

Key words: Chinese fir, dominant height, age-independent method, growth model