Effect of thinning on natural secondary forestry of Pinus massoniana

Set five and six density levels respectively in site index 14 and 12 natural secondary forestry of 23-year-old Pinus massoniana,the effect of thinning on natural secondary forestry of Pinus massoniana after 4 years was studied. The results showed that,the diameter-class distribution of different site index stand before and after thinning showed normal distribution. Before thinning,there were strong differentiation in stand and great disparity in diameter-class. After thinning,the smallest interplant spacing of stand was more close to the average interplant spacing,and the percentage of big diameter-class stand increased,while the percentage of average diameter- class stand increased significantly after 4 years. After 4 years of thinning,when stand density of site index 14 and 12 was greater than 1 500 tree / hm2and 1 950 tree / hm2respectively,DBH dispersion increased markedly compared with the current year of thinning. The growth of average DBH and individual volume decreased with the increase of reserve density,but the growth of stock volume per unit area reached maximum at the suitable density. There existed very significant difference in average DBH,individual volume and unit area volume growth among different reserve density,but there were no significant difference in height and specific weight growth. The growth of average DBH,individual volume and unit area volume with treatment of thinning were higher than CK,the unit area volume growth of site index 14 Pinus massoniana forest was the greatest when the reserve density was 1 500 tree / hm2,which reached 30. 29%. And the unit area volume growth of site index 12 Pinus massoniana forest was the greatest when the reserve density was 1 950 tree / hm2,which reached 24. 38%.