A NEW GENERALIZED HEIGHT-DIAMETER MODEL WITH MIXED-EFFECT FOR PINUS PINASTER AIT. AND PINUS RADIATA D. DON

Abstract

Tree height-diameter (H-D) relationships are important for routine forest assessment. Several H-D relationships have been developed for different species and more are still evolving. This study introduced a new H-D model which was used to predict tree height from 184 and 96 permanent sample plots of Pinus pinaster and Pinus radiata, respectively in northwest Spain. Nonlinear mixed-effect modelling technique was used to fit the generalized H-D model. The mixed-effect H-D model was calibrated using the random effects predicted from one to three randomly selected trees per sample plot. Different indices including root mean square error (RMSE) and adjusted coefficient of determination ( ) were used to assessed the predictive performance of the model. The results show that the new model had  and RMSE of 0.906 and 1.156 m and 0.814 and 1.703 m for P. pinaster and P. radiata, respectively. The calibration response involved the selection of one tree per sample plot – it resulted in a reduction of RMSE by 6.5% and 13.5% for pinaster and P. radiata, respectively.