Objective To quantitatively study the influences of spatial structure on the crown growth of Chinese fir (Cunninghamia lanceolata) in order to realize the visual simulation of Chinese fir crown growth based on spatial structure.

Method Selecting Huangfengqiao State-owned Forest Farm in Hunan Province as a trial plot, the data of crown shape and spatial structure were investigated after different spatial structure units were selected and divided in stand. The under living branch height, crown height and crown width in four cardinal directions were defined as crown shape description factors. Meanwhile, the affecting distance and relative tree height of surrounding trees were defined as horizontal spatial structure parameter and vertical spatial structure parameter. The stepwise regression analysis method was used to analyze the relationships among crown description factors, age, horizontal and vertical spatial structure parameters. As a result, the models of Chinese fir crown growth with different spatial structures were established. According to the fitting method of B-spline curve, the crown shape of Chinese fir was simulated, and 3D Chinese fir tree models in different growth stages were built. Based on the 3D dynamic rendering technology, the visual simulation of Chinese fir crown growth progress was realized.

Result With the stepwise regression analysis on the variable of age, the horizontal and vertical spatial structure parameters, the results shows that there are significant correlations between under living branch height and variables of age and vertical spatial structure parameter. Also, there are significant correlations between crown height and variables of age and vertical spatial structure parameter. Coefficients of determination (R²) of both under living branch height model and crown height growth model are 0.754 and 0.813. It shows extremely significant correlations between crown width and variables of age and horizontal spatial structure parameter. And the R² is 0.623. Based on the crown growth model of Chinese fir and 3D dynamic rendering technology, the crown growth visual simulation of four parts in the cardinal directions is achieved.

Conclusion Using stepwise regression analysis method, the relationships between Chinese fir crown and age, the spatial structure data were analyzed and the growth models of under living branch height, crown height and crown width were built. Combined with 3D dynamic rendering technology and using MOGRE 3D rendering engine, the tree crown visual simulation of Chinese fir was realized based on spatial structure.