Study On Target Tree Density Of Cunninghamia Lanceolata-phoebe Bournei Mixed Forest In Jindong Forest Farm

The near-natural management with the target tree as the core is a sustainable management solution to solve a series of problems such as land quality decline and serious pests and diseases caused by long-term large-scale continuous planting of artificial pure forest.For the near-natural operation method,the full-cycle management target tree density is an important operational parameter.Determining the target tree density at different stages of the forest is of great significance for the scientific management of the near-natural management forest.At present,the research on the tree density of the whole-cycle management target of Cunninghamia lanceolata-Phoebe bournei mixed forest is still in its infancy.This study takes 25 fixed plots of Jindong Forest Farm in Yongzhou City,Hunan Province as the research object,and considers the mixed effect model method.The effect of plotting effect was established to establish the DBH growth model of the Cun,ninghamia lanceolata-Phoebe bournei,the DBH-tree height model and the crown width model,and the full-cycle management target tree diameter and the target trees of each stage of the mixed forest of Cunninghamia lanzceolata-Phoebe bournei.Estimation of density,and then improve the single-plant cutting operation method of mixed forest of Cunninghamia lanceolata and Phoebe bournei,in order to provide a reference and theoretical basis for the scientific management of the mixed forest of Cunninghamia lanceolata-Phoebe bournei.The main research contents and conclusions are as follows:(1)Establish a single-breast diameter growth model of Cunninghamia lanceolata and Phoebe bournei.Taking the four-stage continuous observation data of 16 fixed plots in Jindong Forest Farm as the research object,the multiple-step regression method was used to screen the stand variables.From the model fitting results,the initial breast diameter had a significant impact on the model,so only the initial breast diameter was The independent variable,using the linear mixed effect module in forstat2.0,added the horizontal random effect factor of the plot to construct the DBH growth model based on linear mixed effect of the Cunninghamia lanceolata and Phoebe bournei,and compared the basic model,the model of Cunninghamia lanceolata and Phoebe bournei The coefficient of determination is improved,and the average absolute error and root mean square error are reduced.The final model form is determined as:lnD2=0.1835+0.9528*lnDl+ui(fir,R2=0.9910,MAE=0.0125,RMSE=0.0298),lnD2 = 0.2325 + 0.9463*lnDl+ ui(Phoebe bournei,R2 = 0.9878,MAE = 0.0159,RMSE = 0.0267).(2)Establish a high-diameter model of single-tree tree of Cunninghamia lanceolata and Phoebe bournei.By comparing the three evaluation indexes of coefficient,root mean square error and average absolute error,the Weibull model and the Richards model are the optimal basic models of Cunninghamia lanceolata and P.chinensis.The model is reparameterized by adding the stand variables and the influence is found.The main forest variation factor of Cunninghamia lanceolata and Phoebe bournei is the competition index(CI).On this basis,the random effect of the plot level is added to the model.Compared with the basic model,the determination coefficient of Cunninghamia lanceolata is raised from 0.7916 to 0.8765.At 10%,the average absolute error is reduced by 18%,the determination coefficient of Phoebe bournei is increased by 9%,and the average absolute error is reduced by 15%.The final tree height-diameter model of Cunninghamia lanceolata and Phoebe bournei is as follows:H=1.3+(13.4217/(1+(4.3350+ui+0.2316*CI)*exp(-0.1325*D)))(Cunning-hamia lanceolata,R2=0.8765,RMSE=1.3246);H=1.3+(24.0217+ui)*(1-exp(-(0.0559+0.0058*CI)D))^1.2737(Phoebebournei,R2=0.8453,RMSE=0.4151).(3)Establish a single-wood crown model of Cunninghamia lanceolata and Phoebe bournei.By comparing the evaluation indexes of 11 candidate models,the optimal basic models of Cunninghamia lanceolata and Phoebe bournei were identified as Logistic model and quadratic model,and Hegei competition index(CI)and tree height(H)with high correlation with crown width were selected.),the canopy closure(CD)is added to the basic model,and the accuracy of the model is significantly improved compared with the basic model.On this basis,using the forstat2.0 to add the random effect factor of the sample level to the model for parameter estimation,the basic model is compared.The determination coefficient of Cunninghamia lanceolata increased by 34.6%,the average absolute error decreased by 24%;the determination coefficient of Phoebe bourn increased by 15.1%,and the average absolute error decreased by 28.2%,indicating that there is a certain difference in crown growth of each plot.The final tree height-diameter model of Cunninghamia lanceolata and Phoebe bournei is as follows:CW=(3.4591+ui-0.0026*CI)/(1+(2.7366-0.015*CD+0.0022*H)*exp(0.0712*D))(Cunninghamia lanceolata,R2=0.7012,RMSE=0.5025;)CW=(0.697167 +ui+0.008619*CD)*D^(0.538943+0.004935*H-0.003154*CI)(Phoebe bournei,R2=0.8453,RMSE=0.4151)?(4)Determine the full-period target tree density interval of the mixed forest of Cunninghamia lanceolata and Phoebe bournei.Based on the single-breasted diameter model of Cunninghamia lanceolata and Phoebe bournei,the high-diameter model of single-tree and the single-wood crown model,the tree-density interval of the whole-cycle management target of Cunninghamia lanceolata-Phoebe mixed forest was obtained.In the growth stage,the target tree is 281-458n/hm2?197-247n/hm2,In the competitive growth stage,the target tree growth stage and the stand growth stage,the target tree density range is 90-196 n/hm2,64-77 n/hm2,<58 n/hm2.