Study On Stand Structure Optimization Of Oak Forest At Different Growth Stages Based On Health Evaluation

Quercus species are the first major tree species in natural forests in China,and are also typical zonal tree species and main afforestation tree species in mountainous areas of Henan Province.Quercus has a variety of uses and values,and is the preferred tree species for ecological protection forests.It occupies an important position in China ’s forest resources and has high research value and research significance.Forest health is an important part of forest sustainability.Forest health assessment is the most effective management method for forests.Maintaining and promoting forest health is an important goal of sustainable forest management.Forest health assessment can provide scientific basis for formulating scientific and reasonable management measures.In this study,the mountain area of the Yellow River Basin in Henan Province was taken as the research area,and the oak forests widely distributed in the study area were taken as the research object.A total of 63 survey plots were set up in the study area,and 4 first-level evaluation indexes and 24 second-level evaluation indexes were selected to construct the oak forest health evaluation index system.Three multivariate statistical analysis methods,principal component analysis,cluster analysis and discriminant analysis,were used to analyze and evaluate the forest health status of mountain oak forests in the Yellow River Basin of Henan Province.Stand structure characteristics are an important basis for the function of forest ecosystem.Only with reasonable stand structure can the social,economic and ecological functions of forest ecosystem be fully exerted.In this study,five probability density functions were used to fit the stand diameter distribution,and Kolmogorov-Smirnov(KS)was used to test the fitting effect of five probability density functions.The spatial structure characteristics of oak forests in the study area were analyzed by using angular scale(W),neighborhood comparison(U),Hegyi competition index(CI)and vertical structure parameter(A_Pv),and the spatial structure of oak forests was comprehensively evaluated by comprehensive distance evaluation(CDEV).In this study,the age structure was replaced by DBH structure to study the forest health status and stand structure characteristics at different ages.The main results are as follows:1.The forest evaluation index system of mountain oak forest in the Yellow River Basin was constructed.On the basis of consulting relevant literature and consulting relevant experts,this paper selects four first-level evaluation indexes of stand productivity,soil factor,community organization structure,stability and sustainability according to and fully considering the actual stand status,setting and survey sample data of oak forest in the study area.The corresponding average DBH,average tree height,average branch height,volume per unit area,plant density,soil organic matter,soil total N content,soil total P content,soil total K content,soil bulk density,canopy density,shrub layer Simpson index,shrub layer Shannon-Wiener index,shrub layer Pielou index and herb layer Simpson index,a total of 24 secondary evaluation indicators,constitute the forest health evaluation index system,in line with the scientific,operational,systematic and hierarchical combination of principles.2.Principal component analysis results.The KMO sampling suitability is 0.702,and the Bartlett test p value is 0.000 < 0.01.Both tests show that the sample is suitable for principal component analysis.Seven principal components with eigenvalues greater than 1 were extracted,and the cumulative contribution rate of the seven principal components reached 80.132 %,which could represent most of the information of the survey data.The eigenvalue of the first principal component was 7.974,which explained 33.225 % of the total variation.The characteristic root of the second principal component was 4.177,which explained 17.403 % of the total variation.The characteristic root of the third principal component was 1.969,which explained 8.204 %of the total variation.Since the first principal component has the greatest impact on the whole,according to the principal component factor load matrix,the eight factors that have a greater impact on forest health(the absolute value of the principal component factor load > 0.700)are: average branch height,shrub layer Pielou index,herb layer Shannon-Wiener index,herb layer Pielou index,regeneration layer Shannon-Wiener index,regeneration layer Pielou index,forest fire risk index and total K content.3.Results of cluster analysis and discriminant analysis.According to the cluster analysis method and discriminant analysis method,the 63 plots were divided into 4categories,including 1 plot of class A,22 plots of class B,12 plots of class C and 28 plots of class D,accounting for 1.6 %,34.9 %,19.0 % and 44.4 % respectively.Keywords: Yellow River Basin in Henan Province;quercus;forest health assessment;stand spatial structure;In this study,the forest health status was divided into four grades :’ healthy ’,’ relatively healthy ’,’ sub-healthy ’ and ’ unhealthy ’.According to the classification results of cluster analysis and discriminant analysis,the comprehensive evaluation index was calculated.The comprehensive evaluation index of type A plot was 1.133,that of type B plot was 0.760,that of type C plot was-1.312,and that of type D plot was-0.075.It can be determined that class A,class B,class C and class D correspond to ’ healthy ’,’ relatively healthy ’,’ unhealthy ’ and ’ sub-healthy ’ of forest health evaluation grade,respectively.4.Forest health assessment results of mountain oak forests in the Yellow River Basin of Henan Province.Among the 63 plots investigated,there were 1,22,28 and 12 plots of ’ healthy ’,’ healthier ’,’ sub-healthy ’ and ’ unhealthy ’,respectively.It can be seen that the health status of oak forests in the study area is generally in good condition,but it needs further improvement.According to the age stage,7 of the 17 plots in the first age stage were sub-healthy and 10 were unhealthy.In the 28 plots of the second age stage,the healthy,relatively healthy,sub-healthy and unhealthy grades were 1(3.6 %),7(25.0 %),18(64.3 %)and 2(7.1 %),respectively.In the 18 plots of the third age stage,the healthy,relatively healthy,sub-healthy and unhealthy grades were0,15(83.3 %),3(16.7 %)and 0,respectively.On the whole,the forest health status of the third age stage is better than that of the second age stage,and the second age stage is better than the first age stage.The forest health status of oak forest in the study area tends to be healthy with the increase of forest age(average DBH).5.Structural characteristics of oak forest.According to the K-S test results,for the five probability distribution functions,the p values of 43 plots were all greater than 0.05,indicating that the five probability density functions were acceptable for the fitting effect of the diameter distribution of the plot.On the whole,the fitting effect of Logistic distribution and Lognormal distribution in the five probability density functions is better.The minimum value of the average size ratio of the 43 plots was 0.191,and the maximum value was 0.568,which was close to 0.5.The size differentiation of trees in all plots was weak.By comparing the mean value of the size ratio at different growth stages,it was found that the size differentiation of trees in the stand was low,and the difference in the size differentiation of trees at different growth stages was not obvious.For the horizontal and vertical spatial structure characteristics and competition status of oak forests,with the increase of forest age,the horizontal distribution pattern of oak forests in the three growth stages gradually tends to random distribution,the horizontal competition has an increasing trend,and the vertical competition will gradually weaken.6.Comprehensive evaluation results of spatial structure of oak forest.The maximum eigenvalue of the judgment matrix of the analytic hierarchy process is 4.144,the consistency index CI ’ = 0.048,and the consistency ratio of the judgment matrix CR= 0.053 < 0.1,indicating that the judgment matrix passed the consistency test.The weights obtained are 0.457,0.284,0.121,and 0.138.The objective weights of the four indicators calculated by the entropy weight method are 0.183,0.659,0.092 and 0.066,respectively.The comprehensive weights(CWi)were 0.287,0.643,0.038 and 0.031,respectively.The comprehensive evaluation index CDEV,the value of 35 plots in 43 plots is greater than 0.5,and the maximum value is 0.660,indicating that the spatial structure of the whole plot is general.