| Because most of the Pinus massoniana plantation are pure forests of the same age,their stand structure and density are unreasonable,leading to a reduction in the number and diversity of organisms,aggravation of pests and diseases,decline in fertility,and decline in ecosystem function.Therefore,it is urgent to adjust the stand structure of P.massoniana plantation,which is of great significance for increasing the stability of plantation stands and enhancing the functions of forest ecosystems.This study explored the impact of different management methods and management intensity on the stand structure of P.massoniana,which provided scientific basis for optimizing the structure of P.massoniana plantations and improving stand quality.The experimental site was located in Damaoping State-owned Forest Farm.The test used four types of management methods to treatment the P.massoniana plantation as research objects.The four management methods were non-interference management(CK),crop tree release(6 crop trees per plot,10 crop trees per plot,14 crop trees per plot,18 crop trees per plot)and two kinds of traditional tending management methods according to the number of cutting trees and the intensity of accumulation of the crop tree release.Separately,the number of trees-thinning intensity was 10.2%,18.3%,24.5%,30.0% and the accumulation-thinning intensity was 8.6%,16.1%,24.0%,29.2%.On the one hand,the differences of stand diameter distribution and forest layer distribution characteristics under different management types were compared and analyzed;on the other hand,Voronoi diagram and Delaunay triangulation network were constructed by neighborhood analysis method,and through calculated the five main spatial structure parameters of mingling degree,neighborhood comparison,uniform angle index,competition index and opening degree,and adopted multiplication division method building a comprehensive spatial structure index model,thereby evaluated the influence of different management methods and cutting intensity on the structure of P.massoniana plantation.The results were as follows:(1)Stand diameter: the skewness coefficient of each selective cutting treatment of the crop tree release was greater than 0,the diameter distribution curve showd that the peak was to the left,and the peak appears at 14 diameter steps.The proportion of P.massoniana in the small and medium-sized stands is large,the kurtosis coefficient was less than 0,and the diameter distribution is relatively discrete.The skewness coefficient changes of each treatment of the two kinds of traditional tending management are different.The low-intensity thinning treatment showed a peak right deviation or near normal distribution,while the high-intensity thinning showed a peak left deviation,in most of the treatments,the peak value appeared in the 20 diameter steps.The proportion of P.massoniana in the large-diameter stage increased,and the coefficient of variation of the three management modes was about 30%.(2)Forest layer distribution: crop tree release had a significant effect on the layers density of the up strata(P<0.05),but had no effect on the layers density of middle strata and down strata(P>0.05),while two kinds of traditional tending management all had a significant effect on the layers density of middle tree and lower tree(P<0.05),but had no significant effect on the layers density of upper tree(P>0.05).(3)Mingling degree: after the crop tree release,the mingling degree showd an increasing trend,which help to improve the isolation degree of tree species in the stand.The low thinning intensity had no effect on the mingling degree of the stand,while the high thinning intensity reduced the mingling degree of the stand.(4)Neighborhood pattern and distribution: crop tree release and two kinds of traditional tending management all had little influence on the neighborhood pattern and distribution is still mainly distributed uniformly.(5)Neighborhood comparison: the three management modes also had little influence on the neighborhood comparison,but the dominant degree of different tree species had certain changes.The crop tree release mainly increased the proportion of dominant individuals of P.massoniana and improved the inferior state of Cupressus funebris.However,the proportion of median individuals of P.massoniana increases after two kinds of traditional tending management,and the pressed state of C.funebris also changed.(6)Competition indices: compared with the traditional tending management,the crop tree release could effectively reduce the competition pressure among trees and improve the growth vitality of trees.Under the same contrast treatment,the competition index showed the law of crop tree release<accumulation-tending thinning<number-tending thinning.(7)Opening degree: after the crop tree release,the light condition of the stand had been improved obviously,and with the increase of the intensity of disturbance tree cutting,the forest opening degree had a trend of increasing,and two kinds of traditional tending management had also improved the forest opening degree,but the overall improvement was less than the target tree management.Additionly,under the same contrast treatment,the opening degree value showed the opposite rule with the competition index,that is,crop tree release>accumulation-tending thinning>number-tending thinning.(8)According to the evaluation index of stand spatial structure,it can be seen that the three management methods all improved the evaluation index of stand spatial structure,but the improvement effect of crop tree release t was more obvious,among which the evaluation index of stand spatial structure was the highest under the crop tree release(14crop trees per plot),which indicated that the appropriate interference of tree cutting could promote the optimization of stand structure.Judging from the initial effect,after the target tree management,The diameter distribution,the mixed degree of tree species,the dominant position of single tree,the competitive relationship,the spatial distribution,the size of resources and living space had been improved to some extent,and the stand structure is more reasonable than the traditional tending management. |
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