Study On The Additivity Of Individual Tree Volume Equations Of Dahuria Larch

Individual tree volume model is widely used in forestry production survey.Accurate estimation of standing timber volume is of great significance in forest resources research,timber production and biomass.With the increase of biomass energy,the utilization rate of bark is also increasing,so accurate prediction of stand volume and bark volume becomes particularly important.In order to ensure the consistency of the tree volume and bark volume estimation and improve the prediction precision,the additive model system of Larix gmelinii in Daxing'an Mountains was developed by control method and decomposition method respectively,and four new variant methods were proposed based on them.In addition,Individual fitting method is used as a comparison model.The NSUR method in the proc model of SAS statistical software is used to fit and estimate the parameters.Weighted least squares method is used to eliminate the influence of heteroscedasticity parameter estimation.The fitting results were evaluated using the determination coefficient(R2)and the root mean square error(RMSE);the test results are evaluated by determining coefficient(R2),root mean square error(RMSE),mean error absolute value(MAB),and relative error absolute value(MPB).T-test is used to analyze the differences between different methods.Finally,the prediction results of different diameter classes are compared by the path-order test.The results show that the control method,decomposition method and variant method 4 and method 5 based on control method are all suitable for additive standing volume model;the model fitting goodness of methods 6 and 7 based on decomposition method is general and complex,and they are not suitable for additive standing volume model;T-test between different methods shows that most of the methods are suitable for additive standing volume model.There are significant differences.From evaluation results of different diameter classes testing,for the small diameter classes(5?D<20cm),the models based on control method and decomposition method are better than those based on other models,and decomposition method is better than control method;For the medium diameter classes(20?D<36cm)and large diameter classes(36cm?D),the models based on methods 4 and 5 are better,of which method 4 is better for estimating the volume of barked timber,and method 5 is better for estimating the volume of barked timber.Generally speaking,the additive model system based on control method,decomposition method and methods 4 and 5 can well predict the volume of total volume,inside bark volume,and bark volume,and ensure that consistent prediction results can be obtained.In the specific application,the appropriate additive volume model system can be selected according to the actual situation.