| Forests are the source of human culture and an important place for material acquisition.At the same time,forests also have important ecological functions such as windbreak and sand fixation,climate regulation,carbon sequestration and other ecological functions.The health of forests has long been associated with human beings.Pinus armandii-Abies fabri natural mixed forest in Chayu County is an important part of the forest in southeastern Tibet,which is of great significance to maintain the ecological security and stability of the region.In this study,the natural mixed forest in Cheyingou of Chayu County was taken as the research object.Three parameters of angle scale,mingling degree and neighborhood comparison were selected to analyze the spatial structure of the stand,and the spatial structure of the stand was optimized by simulating artificial harvesting.The evaluation index system is constructed,and the health status is determined by the comprehensive index method.The main conclusions are as follows :(1)Affected by environmental heterogeneity and uneven distribution of trees,the tree layer composition and dominant tree species in the three plots were slightly different.(2)The average angular scale of No.1 and No.3 plots were 0.57 and 0.54,respectively,and the trees were mainly distributed in groups.The average angular scale of No.2 plot was 0.49,which was a random distribution.The average mingling degree of forest stands in different plots showed that the forest community was dominated by moderate-intensity mingling.The value of the average size ratio is about 0.5,and the degree of diameter differentiation is in a moderate trend.(3)The natural mixed forest of Pinus armandii and Abies fabri in Chayu County has reached the late stage of succession.The relationship between different tree species is dominated by coexistence.After simulated artificial logging,the spatial structure of the stand is optimized from the numerical changes of each spatial structure parameter,but it is not statistically significant.Affected by environmental heterogeneity and uneven distribution of trees,the species composition and dominant species of the three plots were quite different.The health degree of Pinus armandii-Abies fabri natural mixed forest in Chayu County is good,and the spatial structure is basically consistent with the characteristics of forest community in the late succession stage.(4)The order of comprehensive weight calculated by analytic hierarchy process and entropy method was as follows : human disturbance degree(0.2097)> DBH basal area(0.1167)> pest degree(0.1079)> natural regeneration(0.0664)> slope(0.0560)> mingling degree(0.0494)> forest fire risk grade(0.0489)> slope aspect(0.044)> angle scale(0.0437)> herb coverage(0.0427)> average tree height(0.0408)> soil moisture content(0.0391)> stand density(0.0386)> humus layer thickness(0.0342)>neighborhood comparison(0.0326)> canopy density(0.0297).In the evaluation index of Pinus armandii-Abies fabri natural mixed forest in Chayu County,the degree of human disturbance,the area of DBH,the degree of pests and diseases,and natural regeneration are the main factors affecting forest health.Improving the forest health index of Chayu County and protecting the ecological function of the forest focus on prohibiting deforestation and overgrazing,improving pest control capabilities,and optimizing forest community structure.(5)The natural mixed forest of Pinus armandii-Abies fabri in Chayu County was divided into five health levels,which were unhealthy [ 0,0.2),sub-healthy [ 0.2,0.4),healthy [ 0.4,0.6),good health [ 0.6,0.8),high-quality health [ 0.8,1).Among the three plots in Chayu County,the health index of No.1 plot was 0.55,which was in a healthy state.The health index of No.2 and No.3 plots was 0.64 and 0.65,which were in good health. |
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