Effect Of Thinning On Growth And Soil Property Of Pinus Massoniana And P.ellionttii Forests

Thinning is an extremely important measure in forest management.To determine optional thinning intensity and evaluate the thinning effects become essential research topics,particularly for silviculture and ecology of plantation forest.In this study,three forest stands at two sites were selected.One stand is a secondary Masson pine?Pinus massoniana?forest located at Hucun Forest Farm in Tongcheng,Anhui Province.Another two stands are Masson pine and slash pine?P.elliottii?plantations located at Gushan Forest Farm in Quanjiao,Anhui Province.The effects of thinning on stand growth and soil properties were investigated after two years of the thinning.The following are the major results.?1?The effect of thinning on the growth of Masson pine.Thinning could effectively promote the growth of Masson pine mature forest,the average DBH increased by 16.30%for high thinning intensity,and by 9.85%for moderate thinning intensity.The effect of thinning on the stand height growth was not obvious.?P<0.05?.The thinning had significant impact on DBH growth,basal area and stand volume increments?P<0.01?.Based on the periodical increment of forest growth after thinning,the thinning effect was ordered by moderate thinning intensity>high thinning intensity>slight thinning intensity>control.Therefore,the moderate thinning intensity is best for mature Masson pine forest.However,the total basal area and stock volume were decreased in the treated stands compared with the control due to the reduction of the density after thinning.?2?The effect of thinning on the growth of slash pine stands.The average DBH was increased by 10.68%after thinning compared with CK,but the thinning had on significant impact on height growth.The average DBH of slash pine was significantly increased?P<0.01?,and the effects were as follows:heavy thinning>moderate thinning>slight thinning>control.The effect of thinning on stock volume was ranked by moderate thinning>heavy thinning>slight thinning>control.The effect of thinning on tree height growth was not significant.Therefore,the heavy thinning was best for DBH growth,while moderate thinning was best for increments of stand basal area and stock volume.?3?Effects of thinning on soil properties.Thinning significantly improved the soil nutrient status of Masson pine and slash pine forests,with the different responses to different thinning intensity.The effect of thinning was obviously greater on 0-10 cm soil layer than on 10-30 cm soil layer.The soil pH,electrical conductivity?EC?and total phosphorus?TP?content were the highest,and TP content was averagely increased by9.68%compared with the control.The soil total nitrogen?TN?,total organic carbon?SOC?,NH₄⁺-N,NO₃^--N and available phosphorus?AP?was increased by 15.84%,18.06%,17.71%,38.46%and 14.20%,respectively,after thinning.The TP content was the highest in slight thinning,which was 18.67%higher than that of the control.The EC was the highest in the control.Soil TN,SOC,NH₄⁺-N,NO₃^--N,AP content was the highest in the heavy thinning,which was,respectively,18.75%,31.56%,46.63%,52.78%and 28.06%higher than those in the control.