| Taking the secondary forest of Quercus species as dominant species in Hunan National Forest Continuous Inventory Sample Land as the research object,the suitable thinning trees were selected through spatial structure index combined with increment,which provided an optimization method for the structural adjustment of secondary forest of Quercus species in Hunan Province.Calculating density index,compiling growth process table of secondary oak forests in Hunan Province,analyzing the growth law of stand,using neighborhood analysis method to create Voronoi map for each sample plot,and analyzing the spatial structure characteristics of stand.According to the four main spatial structure indices of complete mingling degree,uniform angle index,neighborhood comparison and competition index,a comprehensive spatial structure model is constructed based on the principle of multiplication and division.According to the comprehensive spatial structure index of each tree,appropriate thinning trees were selected to optimize the structure.Compatible stand growth and harvesting model is used to simulate the optimal cross-section area,and the optimal cross-section area is used to control the thinning amount.After thinning,the growth vigor of the trees can be improved,and the quality increment can be achieved at the same time of optimizing the stand structure.Taking 2 277 sample plot as an example,by analyzing the tree species structure and diameter structure of the stand,it is concluded that the proportion of oak species in the stand is larger,the diameter distribution of the stand is unreasonable,and the growth of small-diameter trees is restrained.Analyzing the total mixing degree,angular scale,size ratio and competition index of the stand,it was found that the average total mixing degree of the stand was 0.1569 due to fewer tree species and fewer trees of other tree species.The average size ratio of the sample plot approached 0.5 and the average competition index was 6.3774,and the average angular scale was 0.3702,which tended to cluster distribution.Therefore,when choosing thinning,if the comprehensive index of several thinning trees is similar at the same time,the following conditions can be preferred as thinning selection:(1)small-scale oak;(2)complete mingling degree tends to be 0;(3)neighborhood comparison tends to be 1;(4)competition index is greater than 10;(5)uniform angle index is greater than 0.3702.Finally,the area of thinning section was 2.143m2/hm2 according to the compatible stand growth and harvest model.According to other constraints,the thinning intensity was 16.27%and 21 trees were thinned in the sample plot.The number of tree species and diameter rank did not decrease after thinning.After thinning;,the total mixing degree of stand increased by 3.70%,the overall competition intensity of stand decreased by 31.74%,and the angle scale of stand.By 0.46%,the distribution pattern of trees tends to be random,and the spatial structure index of stands increases by 160.12%,which greatly improves the spatial structure of stands.The result of this adjustment makes the stand structure close to the expected direction,but can not meet the expected requirements.It is concluded that long-term and multiple structural adjustments are needed to optimize the structure of such stands to the best state.The more reasonable the stand structure,the higher the stability and the more function it plays.In this study,secondary forests with Quercus as dominant tree species in Hunan Province were taken as the research object.The growth regularity of secondary forests was analyzed,and the optimization scheme of spatial structure was worked out.Combining with the optimization of growth,the optimization model of stand spatial structure and the prediction curve of optimal cross-section area for each age group were constructed.It lays a theoretical foundation for the optimization and regulation of spatial structure of secondary oak forest and the formulation of measures for increasing stand quality. |
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