| As an important forest tending management measure,thinning improves the forest environment by regulating the stand structure,thereby promoting the growth and regeneration of forest stands.The stand structure is the basic feature of the forest ecosystem,and it is the expression of the comprehensive action of various organisms and environmental factors in the stand,which can reflect the state of the stand and its changing laws.The optimization process of stand space structure based on thinning tree selection is based on the construction of the objective function based on the parameters of stand space structure,and the tree with the smallest comprehensive evaluation index value of single tree space structure is selected as the proposed-thinning tree,to achieve the goal of optimizing the spatial structure of the stand.This study took Pinus taiwanensis plantation in Huangbaishan Forest Farm,Shangcheng County,Henan Province as the research object.Plots with basically the same stand conditions were selected for light thinning,moderate thinning,heavy thinning and control treatments,and three fixed plots of 20 m×30 m were set up respectively to investigate and locate trees per tree in the plots.On the basis of studying the unary and binary distribution characteristics of the spatial structure parameters of Pinus taiwanensis plantations under different thinning intensities,and building an optimization model of the stand spatial structure,the evaluation of the optimization effect of the stand spatial structure based on simulated thinning was carried out,which provide some theoretical and technical basis for sustainable forest management in the region.The main research results are as follows:1.Different thinning intensities are all conducive to improving the spatial segregation of tree species in Pinus taiwanensis plantation,among which heavy thinning had the best effect on the improvement of the mingling degree of the stand.The mean mingling degrees of the stands in the lightly,moderately,and heavily thinned sample plots were 0.741,0.740,and 0.804,respectively,all of which were strongly mixed.The mean mingling degree of the stands in the control sample plots was 0.676,which was in the transition from moderate to strong mixedness.Thinning has little effect on the overall size differentiation of stands.The mean neighborhood comparison of the stands was 0.489,0.507,0.507,and 0.504 in the light,moderate,heavy,and control sample plots,respectively,all-around 0.5,the degree of size differentiation of the stand is in the moderate state.2.Different thinning intensities are beneficial to the optimization of the spatial distribution pattern of Pinus taiwanensis plantations,making the trees in the stand tend to be randomly distributed,with light thinning having the best effect on the optimization of the uniform angel index of the stand;The mean uniform angel index of the stands in the light,moderate and heavy thining was 0.507,0.476 and 0.486 respectively,all of which were randomly distributed,while the mean uniform angel index of the control sample plots was 0.473,which belonged to a uniform distribution.Different thinning intensities reduced the intensity of competition among the trees in the stand,making the stand more ample growth space,and with the increase of thinning intensity,the competition intensity of retained trees weakened;The degree of competition between retained broad leaved tree species in the sample plots with different thinning intensities was significantly lower than that in the control sample plots,and the broad leaved species retained in the sample plots after thinning had significantly more growing space than in the control sample plots.3.The study on the binary distribution characteristics of stand spatial structure parameters under different thinning intensities showed that light thinning and heavy thinning increased the spatial segregation of species in the stands on the same neighborhood comparison class and reduced the proportion of stands of the same size differentiation level with the neighboring trees of the same species.Light thinning increases the proportion of dominant and well-mixed trees,while different intensities of thinning reduce the proportion of inferior and poorly-mixed trees.Most of the trees in the same mixed state in all thinning sample plots and control sample plots were randomly distributed,and most of the trees on the same uniform angel index are in the state of strong mixing and extremely strong mixing,and thinning of different intensities reduces the proportion of trees in the same horizontal distribution pattern that is conspecific with surrounding neighboring trees,light thinning increased the proportion of randomly distributed and moderately mixed trees,moderate thinning and heavy thinning increased the proportion of randomly distributed and intensively mixed trees;The majority of trees of the same size differentiation level in the different thinning intensity sample plots and the control sample plots were randomly distributed,and the light thinning reduced the number of randomly distributed and disadvantaged trees in the stand.4.The comprehensive evaluation results of the stand spatial structure of each sample plot under different thinning intensities showed that the different intensities of thinning improved the stand spatial structure,and the light thinning was more conducive to the optimization of the stand spatial structure.The comprehensive evaluation index values of stand spatial structure in the light thinning and heavy thinning sample plots were 1019.870,1293.507,1209.043,and 904.325,1004.257,1175.359,respectively,which were higher than those of the control sample plots of702.640,812.553,748.492.By constructing an optimization model of stand spatial structure,the effect evaluation of simulated thinning of stand spatial structure shows that after 11.9% of the simulated thinning intensity of volume in the sample plot,the degree of spatial segregation of stand tree species and the diversity of forest layers are improved,the growth space of retained trees is more sufficient,and the competition intensity among retained trees is improved,the degree of size differentiation of trees was reduced,the horizontal spatial distribution pattern of stands changed from uniform distribution to random distribution,the comprehensive index of stand spatial structure increased by 232.59%,and the optimization effect of stand spatial structure was obvious. |
PDF Full Text Request