Study on crown profile models for Chinese fir (Cunninghamia lanceolata) in Fujian Province and its visualization simulation

Crown profile models were developed for Chinese fir (Cunninghamia lanceolata) in Shunchang County, Fujian Province. We used data from 360 trees located in 65 pure, even-aged, and unthinned temporary plots. The data were divided into three groups according to site index. Nine models, including models for upper crown, lower crown, and entire crown, were fit; the optimal ones in each group were validated and chosen to estimate crown shape. The optimal models explained at least 70% variability in crown radius (CR). In addition, models for crown width, height above ground to crown base, and height above ground to largest CR were also developed to facilitate the convenient simulation of crown profile models. These three models explained 85.4%, 85.1%, and 86.9% variability. All models also passed the F-test and residual test. The 3D images of a single tree and stands were presented by OpenGL technology on visual c++ platform based on the proposed models. Tree growth was compared and analyzed using crown profile curves under constrained conditions. The analysis results accorded with plant growth.