Site quality evaluation model of Chinese fir plantation in Hunan based on the DBH of average dominant trees
[Objective]This study aims to investigate the impact of site factors on the diameter at average breast height dominant Chinese fir trees in Hunan province and develop a site quality evaluation model with site random effects to address the issue of site quality assessment.[Method]Based on data collected from 509 plots of Chinese fir plantations in Hunan province,significant site factors influencing the DBH growth of average dominant fir trees were identified using quantitative method I in statistical forest software.Initial site types were then established by classifying and combining these influential factors according to standard criteria.The correlation between DBH and age of average dominant trees was fitted using R language,and the optimal basic growth model was selected from four candidate models.K-means clustering was employed to group similar parameter values into distinct site type groups,which were subsequently added as additional random effects into the optimal basic model,resulting in a mixed-effects evaluation model for assessing site quality.[Result]1)Elevation,slope position,soil type,and soil thickness were found to influence the DBH of average dominant Chinese fir trees,with slope position exerting the greatest impact followed by soil type,soil thickness,and elevation.2)Amongst the four candidate basic growth models tested,their fitting accuracy was relatively low(R2=0.641 5-0.642 0).In this study,we selected Mitscherlich molecular formula(R2=0.642 0)as the basic model for evaluating site quality.3)The influence of site effects on our model predictions,nonlinear mixed-effect simulations were conducted incorporating different combinations of individual site factors and their effects;this resulted in an improved determination coefficient ranging from 0.664 2-0.825 8 compared to previous values ranging from 0.641 5-0.642 0.The fitting accuracy was closely associated with the significance of the dominant site factor.The simulation accuracy of the mixed model incorporating site type exhibited the highest value(R2=0.825 8).4)Site types were categorized into 10 groups based on a clustering accuracy standard with a determination coefficient≥0.95.The mixed model utilizing site type groups proved to be convenient for practical application and enhanced modeling accuracy(R2=0.840 9).[Conclusion]Site factors exerted significant effects on the diameter at breast height growth of average dominant Chinese fir trees.Additionally,incorporating site factors as random effects into the hybrid model improved prediction precision,rendering it more suitable for evaluating site quality across diverse site types.
Chinese fir plantationaverage dominant tree DBHsite quality evaluation modelmixed effect
NETL
NSTL
万方数据
