| As a precious tree species for large diameter timber,Phoebe bournei is faced with many problems,such as large area damage of natural forest,slow growth of artificial forest,unreasonable spatial structure of stand,etc.At the same time,with the needs of economic development,the market demand for medium and high-grade large-diameter timber is increasing,but the xXXphenomenon of deforestation has not changed,resulting in the destruction and waste of forest resources has become more serious.There is an urgent need to apply the concept of near natural management and the target tree management method to improve the quality of Phoebe bournei plantation and cultivate high-quality large-diameter timber.The key technology of the target tree management method is to scientifically determine the reasonable target tree density.In order to build a more scientific and reasonable near natural management system of Phoebebournei plantation,this paper takes Phoebe bournei plantation as the research object,uses the data of standard survey,divides the site types,establishes the growth model of DBH of Phoebe bournei,the height curve model of Phoebe bournei,and the crown model of Phoebe bournei.By studying the growth law of Phoebe bournei,the forest is divided on the premise of practicality In the development stage,the target tree density and the target diameter at harvest time of different site types were estimated.In theory,it provides theoretical basis for the near natural transformation of Phoebe bournei precious timber forest,the cultivation of large diameter timber and high-quality stands in Jindong forest farm.The main research contents and conclusions are as follows:(1)The DBH growth model of single tree in Phoebe bournei plantation was established.Based on the measured data,five candidate basic models are used for fitting.Among the five equations,except Korf model and non convergence,the fitting accuracy of the other four basic models for DBH growth of single wood is between 0.6143-0.8062,the average absolute error is between 2.3613-3.7323,and the root mean square error is between 5.3488-10.8558.Among them,logistic equation has the best modeling effect and the highest modeling accuracy(R2=0.8062,MAE=2.3613,RMSE=5.3488).Three site types divided by cluster analysis are used as dummy variables and added to the maximum parameter a of logic equation.It is concluded that the fitting result of adding to a is credible and there is no non convergence,so the modeling effect is the best.The modeling accuracy is the highes t(R2=0.8212,MAE=2.3213,RMSE=5.1871).Compared with the basic model,the coefficient of determination R2 is increased by 1.86%,the mean absolute error MAE is reduced by 1.67%,and the root mean square error is reduced by 3.02%,which shows that the dummy variable model added to parameter a is better than the basic model,and from the parameter of a,the model can reflect the growth trend of DBH under three different site conditions.(2)The height DBH model of a single tree in Phoebe bournei plantation was established.Based on the measured data,11 candidate basic models are used for fitting.Except for strand model,ratkowsky model,pearl model and reed model,the fitting accuracy of the other eight basic models for the height DBH relationship of single tree is between 0.7475-0.7804,the average absolute error is between 1.7706-1.9710,and the root mean square error is between 2.7013-3.1066.Among them,Weibull equation has the best modeling effect and the highest modeling accuracy(R2=0.7804,MAE=1.7709,RMSE=2.7013).Three site types divided by cluster analysis are used as dummy variables,which are added to three parameters and seven forms of Weibull equation.It is concluded that the fitting results on b,a、b,b、c a,b and c are not credible or convergent,and the fitting results on a,c,a and c are credible,not convergent,and the modeling accuracy is better than the basic model.Among them,the fitting effect is the best when added to C,and the modeling accuracy is the highest(R2=0.8349,MAE=1.5295,RMSE=2.1316).Compared with the basic model,the coefficient R2 increased by 6.98%,the mean absolute error MAE decreased by 13.6%,and the root mean square error RMSE decreased by 26.7%.(3)A single tree crown model of Phoebe bournei plantation was established.Based on the measured data,11 candidate basic models are used for fitting.There is no non convergence in the fitting results of all basic models.The fitting accuracy of all basic models is between 0.6805-0.7706,the average absolute error is between 0.6814-0.7731,and the root mean square error is between 0.3883-0.5408.Among them,the fitting effect of the secondary type is the best,and its modeling accuracy is the highest(R2=0.7706,MAE=0.6814,RMSE=0.3883).Therefore,the secondary type equation is selected as the basic model to simulate the single tree crown growth.Using the height of single tree as the stand variable,different parameter s a;B;C added to the quadratic equation of the optimal basic model are fitted,and the fitting results on a;b;c are credible,there is no non convergence,the modeling effect is the best,and the modeling accuracy is the highest(R2=0.7938,MAE=0.6318,RMSE=0.3489).Compared with the basic model,the coefficient R2 is increase d by 2.99%,the mean absolute error MAE is reduced by 7.13%,and the root mean square error RMSE is reduced by 10.14%.It shows that the best crown model fitting effect is good,and can be used to predict the crown growth of Phoebe bournei plantation in Jindong forest farm.(4)Based on the four models,the growth trends of DBH,height,crown diameter and volume of Phoebe bournei in 5-80 years were obtained.It can be concluded from the prediction results that the growth of Phoebe Phoebe bourneiis slow in the early stage,fast in the middle stage,and slow in the later stage,showing "s" type.The DBH growth of different site types tends to be gentle after 60 years,so the DBH of each site at 60 years can be taken as the target diameter.The target diameter of site type 1 is 43cm;the target diameter of site type 2 is 37cm;the target diameter of site type 3 is 45cm.Based on the prediction results and growth trend,the target tree density intervals of five forest development stages are divided.The targe t tree density intervals of three site types of Phoebe bournei artificial forest in the three stages after the start of target tree selection are respectively site type 1:quality selection stage 245-270 plants/hm2,target tree growth stage 131-144 plants/hm2,stand accumulation growth stage 115-127 plants/hm2,site type 2:quality selection stage 318-350 plants/hm2,target tree growth stage 159-175plants/hm2,stand accumulation growth stage 136-149 plants/hm2,Site type 3:298-328plants/hm2 in quality selection stage,156-172 plants/hm2 in target tree growth stage and 136-15 Oplants/hm2 in stand accumulation growth stage. |
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