Parametric prediction models of DBH and height for Cunninghamia lanceolata plantation based on crown width

In order to clarify the relationship between Chinese fir growth and form variables and to improve the forecast precision of harvest, we analyzed data from trees located in 65 Chinese fir (Cunninghamia lanceolata) plots of varying densities with stand age ranging from 6 to 35 years in Fujian Province. Richard’s equation was adopted to develop diameter at breast height (DBH ) and tree height(H)models of Chinese fir. On this basis, the relationship between parameters of the theoretical equation and crown width (CW) were analyzed, and the parameterized harvest forecast model was developed using parameter estimates method through the parameter-CW functions. The model test and residual analysis were carried out for the original models and the parametric models. The relationship between the CW and tree growth is discussed. Results showed that in DBH and parameter a in Richard’s equations of tree height were proportional to CW, parameter b was inversely proportional to CW, and parameters c and CW presented approximately normal distribution. Compared with the traditional theory equations, the parameterized models improve the forecast precision of Chinese fir harvest. The proposed models in this paper are convenient for popularization and application in the future and can indirectly reflect the state of stand factors. The proposed models also provide a mode for analyzing tree competition, photosynthesis, and simulating dimensional visualization of trees.