Study On Forest Structure Of Different Recovery Stages And Optimization Models Of Natural Mixed Spruce-fir Secondary Forests On Selective Cutting

This study is based on the natural secondary forests of spruce-fir in Jingouling Forest Farm,Wangqing County,Jilin Province,the long-term monitoring data of permanent sample plots of spruce-fir forests after 10-20 years under different selective cutting intensities were used,the non-spatial structure characteristics of the stands after 10-20 years of selective cutting were described by species composition dynamics,species diversity dynamics,mortality rate and regeneration rate;Voronoi diagram was used to determine the spatial structure unit of forests,the spatial structure dynamic characteristics of stands in 10-20 years under different selective cutting intensities were analyzed by comparing the spatial parameters such as uniform angle index,mingling,competition index;construct a comprehensive index Q of spatial structure of forest stands,compare and analyze the difference of index after 20 years of selective cutting;optimization models of selective cutting and replanting were constructed,and the application of the spruce-fir forests in Jingouling Forest Farm was carried out to determine reasonable forest management measures and provide a theoretical basis for the scientific management of natural forests.The research conclusions are as follows:(1)During 10-20 years of selective cutting,the tree layer in the sample plots increased from 5-9 species to 8-11 species,and the tree species richness increased with time.In 2018,there were more occasional species than the preliminary survey,which were the key factors leading to the change of tree species composition.The number density of forest stands increased with time.The diversity of tree species in 20 years after selective cutting were higher than that in 10 years after selective cutting.Overall,the diversity index of tree species in the control plots were slightly higher than that in the selective cutting plots.During 10-20 years of selective cutting,with the increase of selective cutting intensity,the mortality rate of trees decreases,which proves that selective cutting disturbance can reduce the death number of trees.The forest regeneration rate of 20%selective cutting intensity sample plots were the highest,and that of 40%selective cutting intensity sample plots were the lowest.The overall mortality rate was higher than the regeneration rate(2)During 10-20 years of selective cutting,the uniform angle index values of different selective cutting intensities did not change much.It was considered that selective cutting had no effect on the overall spatial distribution pattern of the stands in terms of intensity and time scale.And the effect of extremely intensive selective cutting disturbance on the overall mingling of stands were the most obvious.By analyzing the distribution frequency of spatial structure units of trees,it was found that although the mean values of mingling under the selective cutting intensity of 20%were not the highest,but the mingling of sample plots were more uniform,and the distribution of stand was relatively good.(3)The competition index and tree point density were used to analyze the competition of the spruce-fir forests after 10 years of selective cutting.The similar ranking results were obtained,and the validity of the point density in analyzing the forest competition in the Voronoi diagram was verified.During 10-20 years of selective cutting,competition index of stands increased with time.The average competitive pressure of 20%selective cutting intensity sample plots for 20 years were significantly lower than that of other stands,and the forests quality were better.After 10 years of selective cutting,the forest layer richness of 30%selective cutting intensity sample plots were the highest.After 20 years of selective cutting,the change of forest layer tends to be complex with time.The spatial utilization degree of 20%selective cutting intensity plots in vertical direction are higher.After 10 years of selective cutting,the open ratio of the sample plots with 20%selective cutting intensity were the highest,and the illumination condition and light transmittance of the sample plots were better.After 20 years of selective cutting,the sample plots with 30%selective cutting intensity had better illumination conditions and sufficient growth space in the forests.(4)The comprehensive index of stand spatial structure ranged from 0.5146 to 1.0325,and the comprehensive index of 20%selective cutting intensity was the highest,which proves that the weak selective cutting has the best optimization effect on the overall spatial structure of the plots.The forest selective cutting optimization model and the replanting optimization model were constructed and applied to the control plots in 2018.The overall structure of the adjusted stands was optimized.Selective cutting mainly improves the overall competitive pressure and light environment of the plots;and replanting focuses more on optimizing the distribution pattern and vertical distribution of the stand.The combination of selective cutting and replanting has practical significance for guiding the sustainable management of natural secondary forest of spruce-fir,and the state of the stand is improved and restored.