The purpose of this study was to explore the effects of mixing ratio on growth and competition for Betula alnoides and Castanopsis hystrix, so as to provide evidences for rational mingling and further efficient management of their mixture.

The growths of B. alnoides and C. hystrix were investigated in 6-year-old mix trial plantations in Pingxiang, Guangxi, which included five treatments: monoculture of each species and mixtures of B. alnoides and C. hystrix with ratio as 1∶1, 1∶3 and 1∶5. The intraspecific and interspecific competition index of both species were calculated with Hegyi's competition model, the differences of tree growth and competition among these treatments were compared, and correlation between tree growth and competition was clarified.

Compared with monoculture, the mixing treatments significantly promoted tree height, diameter at breast height (DBH), crown width (CW), basal area at breast height (BA), crown length (CL), crown volume (CV) and crown surface area (CSA) of B. alnoides; and for C. hystrix, DBH, CW, CL, CV and CSA of 1:1 mixing treatment were significantly higher than those of its monoculture. The intraspecies competition index decreased significantly for B. alnoides while increased for C. hystrix with increasing proportion of C. hystrix; the highest interspecific competition index were found in treatments of mixing ratio of 1∶1 for B. alnoides and 1∶3 for C. hystrix. The intraspecific competition indexes were in significantly negative correlation with DBH, tree height, CW, BA, CL, CV, CSA, and were significantly positively correlated with tree height to diameter ratio (H/D) and crown ratio for both species; and the interspecific competition indexes were significantly and negatively correlated with DBH, tree height, height to crown base (HCB), CW, BA, CV, CSA for B. alnoides, while were only in significantly negative correlation with tree height for C. hystrix.

As a whole, mixing ratio of 1∶1 was recommended in the practice for establishing mixture of B. alnoides and C. hystrix in southern China.