Evaluation of Nonlinear Height-Diameter Models of Two Important Species of Turkish Pine (Pinus brutia) and Mediterranean Cypress (Cupressus sempervirens var. horizontalis), in the Planted Forests

Knowledge about the relationship between tree height (H) and diameter at breast height (D) is crucial for forest planning, monitoring, biomass estimation, and forest stands dynamics description. In this study, 20 different height-diameter models were evaluated to estimate accurately the height of the trees of Pinus brutia and Cupressus sempervirens var. horizontalis species in Arabdagh region (north-east of Golestan province). Required data for cypress and pine species were collected from 114 and 98 circular sampling plots, respectively, using a systematic cluster survey network with cluster spacing of 400 * 600 m. Species characteristics such as diameter at the breast height of all trees (greater than 7.5 cm) and trees height were measured and recorded in all sample plots. Overall, 389 and 299 pairs of height-diameter observations were collected for cypress and pine, respectively. The 75 percent of the data were used in the modeling process and the rest data were used to evaluate the models. The fitness of the models was evaluated using statistical criteria of RMSE% and R2. The results showed that for cypress and pine, the R2 ranging from 0.55 to 0.59 and 0.50 to 0.51 and the RMSE% varied from 15.32 to 22.87 and 11.09 to 16, respectively. At the end, the models of Sibbesen, Michaelis-Menten, Power, Prodan, and Chapman-Richards for the Cypress, and the Gomperz, Korf, Weibull, Michailoff, and Ratkowsky models for the pine species were better able to estimate trees height.