Effects of thinning retention density on growth and wood species structure of Chinese fir plantation based on large-diameter timber cultivation

The influence of thinning reserved density on the growth, diameter distribution and timber assortment structure of Chinese fir plantation based on large-diameter timber cultivation was explored, which provided some scientific theoretical basis and technical support for thinning density control technology of directional cultivation of Chinese fir large-diameter timber.

The 9-year-old Chinese fir plantation in Guanzhuang state-owned forest farm, Shaxian county, Fujian province was taken as the research object, and three treatments, namely high thinning reserve density (H: 2 250 plants /hm²), middle thinning reserve density (M: 1 800 plants /hm²) and low thinning reserve density (L: 1 200 plants /hm²), were set for continuous observation for five years.

1) The DBH of the stand increased with the decrease of thinning reserve density, with L > M > H, and there were significant differences (P < 0.05). When the age of the stand was 11 years, there was a very significant difference (P < 0.01), and the effect of thinning on tree height was not significant; 2) the volume of individual tree increased with the decrease of thinning reserve density, showing L > M > H, and the volume of stand showed H > M > L; 3) The total timber output increased with the increase of thinning reserve density, which was H > M > L; The total timber yield increased with the decrease of thinning retention density, which was L > M > H; 4) The output of small-diameter timber increased with the increase of thinning reserve density, showing that H > M > L, and H was significantly greater than L (P < 0.05), which first increased and then decreased with the increase of forest age, and the output rate of small-diameter timber showed that L > M > H. The output of medium-diameter timber decreased with the increase of thinning reserve density, increased with the increase of forest age, and the output rate decreased with the increase of thinning reserve density. The output and yield of large-diameter timber increased with the decrease of thinning retention density, and L was significantly greater than H (P < 0.05).

Tending thinning can promote the growth of Chinese fir plantation, optimize the stand structure and benefit the cultivation of large-diameter trees.