Construction And Application Of Individual Tree Crown Length Model Of Larix Principis-Rupprechtii Natural Forest

Crown length is an important indicator to describe the vertical structure of the crown and reflect the competition of forest trees.Therefore,the establishment of a crown length model is of great significance to understand the crown structure and the growth potential of the stand.Taking Larix principis-rupprechtii natural forests in Pangquangou Nature Reserve and Wutai Mountain Boqiang Forest Farm in Shanxi Province as the research objects,the methods of basic model selection,re-parameterization model,random forest model,dummy variable model and mixed effect model were used to construct individual tree crown length model;and on this basis,according to the correlation between crown length and crown ratio,crown surface area and crown volume,the simultaneous equations of crown ratio,crown surface area and crown volume are constructed by introducing the tree height curve and crown width model of the same data source was compared and analyzed with the separately established models of crown ratio,crown surface area and crown volume allometric growth model to verify the feasibility of the application of the crown length model.It provides a theoretical basis for the research on the crown structure,stand growth and harvesting,and precise improvement of forest quality of Larix principis-rupprechtii.The main research contents and conclusions of this paper are as follows:(1)The Logistic formula of three parameters in the 9 candidate models is the optimal crown length-diameter at breast height candidate model;on this basis,multiple stepwise regression analysis is used to screen out the basal area per acre in trees that were larger than the subject tree(BAL)and the Storey(Storey)and the average height of dominant trees(HDOM)in the plot to construct a crown length re-parameterization model;use the random forest method to construct a crown length random forest model;consider the differences between different regions and plots on the crown length growth,constructing a dummy variable model of crown length with regional dummy variables and a mixed effect model of crown length with random effects of plots.Comparing the fitting accuracy of the crown length basic model,the re-parameterized model,the random forest model,the dummy variable model and the mixed effect model,it can be seen that the mixed effect model is the best fitting model for the crown length.Compared with the basic model of crown length,The coefficient of determination(R2)is improved by about 33.99%,the root mean square error(RMSE)is reduced by about 28.02%,and the mean absolute error(MAE)is reduced by about 32.71%.(2)On the basis of the established crown length model,according to the relationship between crown ratio,crown surface area,crown volume and crown length,the tree height curve and crown width model from the same data source were introduced,and the fitting accuracy of the crown ratio,crown surface area and crown volume model was deduced by using the method of simultaneous equations.In addition based on the relationship between crown length,crown surface area,crown volume and other tree factors an allometric growth model was established,and the accuracy of the model established with the simultaneous equations was compared and analyzed.To verify the feasibility of the application of the crown length model.The results showed that the crown ratio simultaneous equations model(R2=0.4235,RMSE=0.1352,MAE=0.0952)was significantly improved compared with the basic model(R2=0.1527,RMSE=0.1656,MAE=0.1346),and the mixed effects model(R2=0.4529,RMSE=0.1333,MAE=0.1038)the accuracy is almost the same;the crown surface area allometric growth model(R2=0.9999,RMSE=0.0766,MAE=0.0334)and the simultaneous equation model(R2=0.9999,RMSE=0.0956,MAE=0.0055)there is no significant difference in fitting accuracy;the accuracy of the crown volume allometric model(R2=0.8467,RMSE=3.3944,MAE=2.4760)and the simultaneous equation model(R2=0.8459,RMSE=13.7688,MAE=9.1551)change not obvious.Therefore,the application of the crown ratio,crown surface area and crown volume model derived based on the crown length model is feasible.