Effect of Thinning on Growth of Secondary Betula luminifera Forest

Thinning experiment of secondary Betula luminifera forest located on Chadian Township of Zhijin County in Guizhou Province were carried out herein.The result showed that the thinning had different effects on the breast-height diameter,height and individual volume growth of the stands.All effects of heavy thinning on them achieved significant level.Effects of moderate thinning on breast-height diameter and height growth were not significant,but effect on individual volume growth gained significant result.Growth stock of each experiment stand presented a gradual increase tendency.Growth stock of heavy thinning stand was the highest,moderate thinning stand was secondary,and no thinning stand was the lowest.At the 10th years after thinning,average breast-height diameter,height,individual volume and growth stock of heavy thinning stand were more than that of thinning-free by 31.3%,28.2%,116.5% and 44.7%,respectively,however,that of moderate thinning stand increased only by 10.0%,9.3%,30.8% and 23.3%,respectively.Under medium site condition in the tested areas,it was very necessary that thinning of suitable intensity was carried out for secondary Betula luminifera forest at 7-year-old and density of more than 7,630 stems/hm2.To cultivate timber-forest,the suitable thinning intensity based on tree quantity should be not less than 50 percent.