Close-to-nature silviculture of Chinese fir plantations mixed with Phoebe bournei is the widely silviculture mode in China. Exploring the effects of close-to-nature silviculture mixed with P. bournei in Chinese fir plantations on forest growth and timber assortment output of Chinese fir provides insight into selecting suitable silviculture mode for large-size timber production.

Based on the Chinese fir forests mixed with P. bournei in Chenzhou Xishan Forest Farm, Hunan, four treatments were set in the study, including three close-to-nature silviculture modes mixing with P. bournei and one control mode. The diameter at breast height, tree height, crown width, tree volume and stand volume of Chinese fir as well as the timber assortment output were analyzed and compared under different modes.

Compared with the control mode, other than the stand volume, the mean diameter at breast height, mean tree height, mean crown width and mean tree volume of the three close-to-nature silviculture modes were all greater than those of the control mode. There were significant differences between diameter, tree height, crown width, tree volume and stand volume (P<0.01). Moreover, the timber assortment output rate of Chinese fir was also significantly different (P < 0.01). The large-size timber output and rate of mode T1 were the largest, followed by mode T2, T3, and CK, and the output and rate of large-size timber of Chinese fir decreased with the increase of the proportion of Chinese fir. The large-diameter timber output of Chinese fir was positively correlated with mean diameter, dominant height of stand and mean crown width, but negatively correlated with the retention density of Chinese fir.

Compared with pure Chinese fir stand, the close-to-nature silviculture modes can significantly promote the growth of Chinese fir. Close-to-nature silviculture mode mixed with P. bournei in Chinese fir forests (T1: the ratio of Chinese fir and P. bournei is 3∶7) is conducive to cultivating large-size timber of Chinese fir. A lower retention density of Chinese fir is helpful for optimizing the timber assortment structure and cultivating large-size /super-large-size woods of Chinese fir.