Intraspecific competition in a Cunninghamia lanceolata plantation with different age and diameter classes

To test the hypothesis that stand age and diameter class in a Cunninghamia lanceolata plantation affected competition intensity, Hegyi's distance-dependent competition index model and analysis of variance(ANOVA) were used in the analysis for and discussion of the relationship between stand age, diameter class,and competition intensity. Results of the ANOVA demonstrated a highly significant effect(P0.01) of both stand age and diameter class on competition intensity. The average intraspecific competition intensity between10 and 25 years decreased with increasing stand age, and after 25 years continued to decrease but at a decreasing rate. With an increase in diameter class from 0-20 cm, the average intraspecific competition intensity also decreased, but it exhibited little variation when larger than 20 cm. The exponential function IC= ae-bx could be used to represent changes in competition intensity for stand age and diameter class with ICi= 73.761 3D-0.978 3. Thus, competition intensity was closely related to stand age and diameter class providing an important basis for scientifically and effectively carrying out the management of Cunninghamia lanceolata plantations.