Simulation model of crown profile for Chinese fir (Cunninghamia lanceolata) in different age groups

In order to model the crown profile by mathematical simulation for Chinese fir (Cunninghamia lanceolata) in different age groups, this study utilized the nonlinear regression method to select the effective variables, i.e. the relative crown radius (RCRj) as the dependent variable and relative crown length (RCLj) as the independent variable for the crown profile model. Using data from 1 485 measurements of crown radius with 297 sample trees of Chinese fir at Shunchang County of Fujian Province, the optimal crown profile models in the different age groups were established based on 8 kinds of foundation models. The analysis of error and residual, model test and biological evaluation were carried out for the optimal crown profile models. Results showed that the optimal crown profile models of the young growth, half-mature, and near-mature and mature forests were the Cubic, Poly4 and GaussAmp, respectively. The crown profile models developed can be used to estimate the crown profile which only requires to measure the total tree height, the largest crown radius and length. Such models are important components of growth and yield models, and are also crucial for assessing the level of competition, forest microclimate and biodiversity.