Effects of different intensity of thinning on the improvement of middle-aged Yunnan pine stand

In the survey of a 25 year old Yunnan pine artificial forest in Xujiashan plot in Lufengcun forest farm of Yuliang County was carried out in 2008.The forest was consided as low guality by evaluating its stand density,average DBH of the trees,area covered by single trees and the rate of eracted died trees inside plot,thus tending thinning was adopted as a major compliment of improvement.Four transects(three plots and one control) were set up oriented to southeast with treatments of 4 different intensity of thinning under the original density of the forest.The thinning was taken by a unit of 1 hm2,and the transects were 30 m × 30 m(900 m2) and trees were approximately identical.The thinning intensities were 40%(plotⅠ),30%(plotⅡ) and 20%(plotⅢ) 0%(control),respectively.The second survey was taken after the thinning finished and the third survey was carried out one year later.The results show that compared to ther control,the trees of all treatment the average DBH(diameter at breast),minimal DBH and the lowest concentrated DBH range had been improved significantly after the thinning,and the average height of the trees was also heightened.Among 4 intensities of thinning,the better performances were that of thinning intensity of 40% and 31.5%.While when they were 20.5% and 31.5%,the stands had tendency of becoming into mixed forest of needle and broadleaf trees and mainly of Yunnan pine,this might accelerate the succession and while in control plot,only the shnub and grass were cleared in addition with some broad-leaf trees,thus the pine trees presented with a left shewed normal distribution,showing an uneven and natural slack DBH distribution.Through the thinning intensity of 31.5%,the forest reached lowest mortality.It is concluded that the quality of the stand improved greatly by thinning,and specifically the effects were notably in low production forest of Yunnan pine,thinning intensity with 31.5% is recommended.