Nonlinear Mixed Effect Growth Prediction Model Of Quercus Glauca Under Climatic Influence Based On R Language

The growth and development of forest have a direct impact on the ecological benefits of forestry.The study of effective forest growth model is conducive to the sustainable management of forests.The impact of climate change on the global forest ecosystem is very obvious,it not only affects the temperature,precipitation,CO2,humidity and sunlight visibility,but also affects soil quality,humus,and indirectly affects biodiversity,phenology and stand structure.In this paper,a nonlinear mixed effect growth prediction model of Cyclobalanopsis glauca forest in Lutou experimental forest farm of Central South University of Forestry and Technology under the influence of climate based on R is constructed.The growth trend of Cyclobalanopsis glauca under the future three climatic conditions is forecasted.The specific research work includes the following aspects.First,the paper presents data preparation and analysis.Based on the data of height,volume,DBH and age of 18 oak trees,and the past and future climatic data of RCP2.6,RCP4.5 and RCP8.5 is collected and downloaded from the climate AP platform.Then the principal component analysis of climate data is carried out to get the number of principal components and the score of principal components.The principal component score is used as an independent variable to fit the nonlinear growth curve in order to forecast the growth trend of the model of Cyclobalanopsis glauca.Then,the paper constructs the model of the nonlinear mixed effect growth prediction model of Cyclobalanopsis glauca forest.The proper growth equation is selected first,and then the parametric efifect is determined.The growth equation with mixed parameters is fitted by nonlinear regression and the parameters are tested.After all the possible forms of the random effects of the mixed model are obtained,the R function package in nlme is used to fit several families of nonlinear mixed effects models.Compare their AIC,BIC,LL with the P values of the estimated parameters,and choose an optimal nonlinear mixed effect model from the results.Then,the model parameters are tested.Finally,three nonlinear mixed efiFect growth prediction models based on DBH,volume and tree height is established.Finally,the growth trend under the future three climatic conditions is predicted by using the prediction model.The results show that RCP8.5 climate conditions are the most favorable for the growth of trees,followed by RCP4.5,and RCP2.6 climate conditions are the least favorable for the growth of trees.