The Stand Structure Of Different Density Cupressus Funebris Artificial Forests Reconstructed By Thinning

The Cupressus funebris plantation is widely distributed in the hilly area of central sichuan（basin）.As the main type of shelterbelts in the middle and upper reaches of the Yangtze River,which were built in the 1980s,because of the high initial planting density and the construction of pure forest,there are some serious problems,such as unreasonable stand structure,poor natural regeneration,poor stand stability,low wood yield,soil fertility decline and low soil and water conservation function,it is urgent to carry out stand transformation and structure control.Therefore,in this study,three plantations with different densities(1200 plants per hm^-2 of low density,1900 plants per hm^-2 of medium density and2600 plants per hm^-2 of high density)were planted in 1995 in the state-owned forest farm of Qiqu Mountain,C.funebris,China,in October 2022,the stand structure was regulated by tending thinning,and four stands with different stand densities were set up with different thinning intensities of 0%,10%,20%and 30%,with the non-thinning stand（thinning intensity of 0%）as the control,3 repeated plots were set up for each treatment,and a total of36 plots were set up.The effects of non-spatial structure（diameter structure and forest layer structure）and spatial structure（mingling degree,angle scale,size ratio and openness degree）were discussed,the variation of stand structure with thinning intensity was analyzed,and the spatial structure of stands under different thinning intensity was comprehensively evaluated in order to provide reference for the optimization and adjustment of plantation structure in C.funebris.The results were as follows:（1）The peak values of diameter order distribution of low,middle and high density stands were 16,12 and 8 respectively,the proportion of small diameter order of middle and high density was large,the skewness of diameter distribution of each density was greater than 0,the diameter distribution curve showed that the bigger the density,the more left the curve.The peak degree of diameter distribution curve was less than or close to 0 The low-density and medium-density forests were mainly upper-layer forests,the high-density forests were mainly upper-layer and middle-layer forests.After thinning,the diameter distribution of stands of all densities moved to the direction of larger diameter,and the peak value of the diameter of low density stands did not change,while the middle and high density stands were treated with thinning intensity of 20%and 30%,respectively,the deviation of the diameter distribution curve decreased with the increase of thinning intensity,and the diameter distribution was close to the normal distribution,and the peak degree increased with the increase of thinning intensity,the diameter distribution of stand is more concentrated,the variation coefficient decreases,and the dispersion degree of stand diameter distribution decreases.（2）Under different stand densities,the mingling index of stand increased with the increase of thinning intensity.In low-density stands,the mixed degree of 20%and 30%thinning intensities was significantly higher than that of 10%and no thinning.The mingling index of medium-density stands was significantly higher than that of other treatments.In high-density stands,only 30%thinning intensity treatment could significantly increase the mingling index of stand,but the difference between the other treatments was not significant.In low-density stands,the increase of stand uniform angle index was not significant among different thinning treatments,but in medium-density stands,the increase of stand uniform angle index was significant under 20%and 30%thinning treatments.In high-density stands,the stand uniform angle index was significantly increased after every thinning treatment,but it was not significantly increased between 10%,20%and 30%thinning intensity treatments.There was no significant difference in stand neighborhood comparison of different stand densities,and there was no significant difference in different thinning intensities.In the low-density stands,the stand opening degree under the treatments of 10%,20%and 30%thinning intensity was significantly higher than that of the non-thinning stands,and the effect of 30%and 20%thinning intensity was significantly higher than that of 10%thinning intensity,however,the effect of thinning intensity of 20%and 30%was not significant.In the medium-density stands,the stand opening degree with 30%thinning intensity was significantly higher than that with 10%thinning intensity and without thinning intensity.There was no significant difference between 30%and 20%,20%and 10%thinning intensities.In the high-density stands,the stand opening degree was higher with 30%thinning intensity than with no thinning,10%and 20%thinning intensity,but there was no significant difference between the stand opening degree with no thinning,10%and 20%thinning intensity.（3）In low-density stands,the effect of 20%thinning intensity treatment on the ratio of high mixing degree-random distribution,high mixing degree-dominant state,high mixing degree-good light condition and random distribution-dominant state was significant In medium-density stands,there is no uniform law on the increasing or decreasing effects of different thinning intensities on different combinations of stands,the effects of 30%thinning intensity treatment on the proportion of individuals with high mixing degree-random distribution,non-random distribution-inferior status and non-random distribution-poor illumination condition were obvious However,thinning did not significantly reduce the proportion of individuals with mixed degree-non-random distribution,low mixed degree-inferior state and inferior state-inferior light condition.（4）In low and high density stands,the spatial structure evaluation indexes of 20%and30%treatments were significantly higher than those of no thinning stands,and the spatial structure evaluation indexes of 20%treatments were significantly higher than those of 10%treatments.There was no significant difference between 10%and no thinning,between 20%and 30%,and between 30%and 10%.In the medium-density stands,the spatial structure evaluation indexes under 20%and 30%thinning intensities were significantly higher than those without thinning,and there was no significant difference between 10%thinning intensities and without thinning.There was no significant difference in the evaluation indexes of stand spatial structure under the treatments of 10%,20%and 30%thinning intensities.To sum up,the spatial structure assessment indices of C.funebris plantations with different densities can respond positively to tending thinning and increase with thinning intensity,the evaluation index of forest spatial structure of low-and high-density stands was the highest at 20%thinning intensity,while that of medium-density stands was the highest at 30%thinning intensity.However,there was no significant difference between 20%and30%thinning intensities under different densities.Therefore,20%thinning intensities would be more beneficial to the improvement of spatial structure quality of C.funebris plantations.