| One of the main influencing factors is the overall quality of forest,the growth rate of forest,the speed of forest succession and thinning.In order to accelerate the positive succession of forest,appropriate tending and thinning measures should be taken to improve the overall quality of forest.In this paper,16 plots with different thinning intensities(control,low intensity,medium intensity and high intensity)in different succession stages(young forest,middle age forest,near mature forest and mature forest)of Larix gmelinii secondary forest in Daxing'an Mountains were set up.23 indexes related to soil layer,canopy structure and stand spatial structure were measured in the plots,and the soil canopy structure was constructed The change rules of soil layer,canopy layer and stand spatial structure were discussed.The relationship among the three index systems was explored,and the best thinning intensity of soil,canopy and stand spatial structure of Larix gmelinii natural secondary forest in different succession stages was screened by using grey correlation method.The research results provide important scientific basis for the further realization of sustainable forest management in Daxinganling region.(1)In soil layer,soil bulk density,humidity,and capillary porosity in the same succession stage showed a trend of rising firstly and then decreasing with the increasing thinning intensity;non capillary porosity increases first and then decreases,while in mature forest is the smallest and middle age forest is the largest;the total soil porosity and water holding capacity also show a trend of increasing gradually in mature forest with intermediate cutting strength The results show that the gray correlation degree of soil fertility is from large to small R2(1.35)>R1(1.33)>R3(1.32)>R0(1.28)>N2(1.25)>N1(1.23)>N3(1.22)>N0(1.2)>M2(1.19)>M3(1.18)>M1(1.17)>M0(1.15)>Y2(1.13)>Y1(1.12)>Y3(1.1)>Y0(1.07).the higher the soil fertility of forest land in different succession stages.It can be concluded that the soil fertility of medium intensity tending and thinning mature forest is the highest,and it can play a better ecological function and promote the growth of trees.(2)In the study of canopy structure,the leaf area index of various plots was the lowest in R3(high thinning intensity mature forest)and Y0(young forest control)sample.The results showed that the degree of opening of different land also increased with the increase of thinning intensity in each succession stage,the largest in R2(medium thinning intensity mature forest)plot,and the smallest in Y0(young forest control);the leaf area index and average leaf inclination of all kinds of land did not change with the succession and the intensity of thinning,and the total radiation on the crown of 16 samples was very close,It can be concluded that the medium thinning intensity can promote the growth of canopy and the change of structure.(3)In the spatial structure of stand,the isolation degree,horizontal distribution pattern and the degree of size differentiation of Larch natural secondary forest in Daxing' anling were analyzed.It can be seen that the natural secondary forest of Larch in Daxing' anling is mainly mixed with zero degree and weak degree,and the average angular scale of all places is between 0.415-0.897,and most of the trees in the experimental area are randomly distributed.The distribution of the ratio of size to size of trees in the experimental area is relatively uniform,most of the individuals are in the mean position.Therefore,it can be seen that the tending measures of different thinning intensity have no significant influence on the differentiation degree of forest size in all areas.The grey correlation evaluation is determined by grey correlation method.The results show that the grey correlation degree between canopy and stand growth is R2(0.93)>R3(0.92)>R1(0.91)>N3(0.91)>N2(0.90)>M3(0.90)>N1(0.89)>N0(0.88)>M2(0.88)>M1(0.87)>R0(0.87)>M0(0.83)>Y3(0.82)>Y2(0.81)>Y1(0.78)>Y0(0.76).The results showed that the best growth rate of soil fertility was the highest in mature forest with medium thinning intensity.(4)Three functional indexes of soil layer,forest canopy structure and stand spatial structure influence each other.According to the measurement of 23 functional indexes of soil layer,forest canopy structure and stand spatial structure,the scores of comprehensive evaluation results from high to ground are as follows:R2(0.96)>R3(0.94)>R1(0.93)>R0(0.92)>N2(0.91)>M2(0.91)>N3(0.9)>M3(0.9)>N1(0.9)>NO(0.9)>M1(0.89)>M0(0.88)>Y2(0.88)>Y3(0.87)>Y1(0.87)>Y0(0.86).It is concluded that the mature forest with moderate thinning intensity is most beneficial to the overall growth of trees. |
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