Siavash Kalbi;Asghar Fallah;Pete Bettinger;Shaban Shataee;Rassoul Yousefpou

Sari Agriculture and Natural Resource University;;Univ. of Freiburg#TAB;*University of Georgia;Gorgan Agriculture and Natural Resource University

Random effects;Tree height;Calibration;Sangdeh forest;Chapman-Richards model;Oriental beech;DIAMETER MODELS;GROWTH;PLANTATIONS;EQUATIONS;STANDS;PINE;POPULATION;PORTUGAL;CURVES;SPAI

Height-diameter relationships are essential elements of forest assessment and modeling efforts. In this work, two linear and eighteen nonlinear height-diameter equations were evaluated to find a local model for Oriental beech (Fagus orientalis Lipsky) in the Hyrcanian Forest in Iran. The predictive performance of these models was first assessed by different evaluation criteria: adjusted R-2 (R-adj(2)), root mean square error (RMSE), relative RMSE (%RMSE), bias, and relative bias (%bias) criteria. The best model was selected for use as the base mixed-effects model. Random parameters for test plots were estimated with different tree selection options. Results show that the Chapman-Richards model had better predictive ability in terms of adj R-2 (0.81), RMSE (3.7 m), %RMSE (12.9), bias (0.8), %Bias (2.79) than the other models. Furthermore, the calibration response, based on a selection of four trees from the sample plots, resulted in a reduction percentage for bias and RMSE of about 1.6-2.7%. Our results indicate that the calibrated model produced the most accurate results.