Generalized Algebraic Differential Growth Model of Dominant Height for Larix olgensis Plantations
[Objective]Taking Larix olgensis plantations as the research object,this study aims to explore the difference of site quality between different site types,grade division of site from classification of site types is realized,and accurately evaluate the site quality of L.olgensis plantations.[Method]Based on the sample plot data by the national forest inventory and the forest management inventory in Jilin Province,a difference model for stand dominant height growth was constructed by generalized algebraic difference approach.The dominant site factors significant affecting dominant height growth of L.olgensis were screened by partial correlation analysis and formed the site types(ST).Site type groups(STG)is formed by clustering site types based on K-Means algorithm,and the ST and STG are taken as random effects to construct the dominant high growth mixed effect model respectively,adding exponential function,power function and constant plus power function to eliminate heteroscedasticity,autocorrelation of order 1,compound symmetry and autocorrelation-moving average,three structures were used to consider the autocorrelation,the optimal mixed effect model was selected and carried out the site rank according to the site type groups corresponding to the dominant height at 30 years.[Result]The optimal difference model M1.1 evaluation index adjusted coefficient of determination(R2a)=0.865,relative root mean square error(rRMSE)=7.756％.The site factors that had significant effect on stand dominant height(P＜0.01)and their partial correlation coefficients were elevation 0.379,soil thickness-0.247,humus thickness 0.190,slope position 0.113,slope degree 0.067,respectively,the first three factors were identified as dominant site factors,and 45 site types were formed.5 site type groups were obtained from 45 site type clusters,the optimal mixed effect model M1.7 considering site type groups,AIC(Akaike information criterion)is 4 402.492 and BIC(Bayesian information criterion)is 4 451.014,decreased by 7.42％and 7.04％compared with AIC and BIC of M1.1 respectively.Divided into 5 site grades by using M1.7,the dominant height at 30 years are 18.7,17.6,16.2,14.4,12.8 m in turn.[Conclusion]Richards,Korf and Hossfeld are more suitable than other base models to derive difference models.Elevation,soil thickness and humus thickness are the dominant site factors affecting the growth of dominant height for L.olgensis.The corresponding table of site types and site grade is obtained.
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