Evaluating the Effect of Some Physiographic Factors on Growth Models of Hornbeam (Carpinus betulus L.) in Arasbaran Forest

The current study aimed to investigate changes in growth models of hornbeam (Carpinus betulus), as the most abundant species in Arasbaran forest, at different altitude ranges and aspects. Sampling was performed in one-hectare plots at the altitude range of 1200 to 1500 meters and hornbeam trees were measured on the diameter at the breast height (DBH), total height and the diameter of crown canopy. Data analysis was carried out by Nonlinear Regression Models and the best models were fitted based on maximum correlation coefficient, coefficient of determination, minimum standard error and Akaike coefficient for the relationship between diameter (independent variables), and height, basal area and the crown canopy (dependent variable). Results showed that there was a positive correlation between DBH, height, and basal area of trees (r = 0.994) but DBH and crown canopy had a negative correlation. In addition, there was a significant difference in height and crown canopy of the trees across altitudes and aspects. The results of nonlinear models revealed that Exponential Linear Model, Rational Model, Heat Capacity, Sinusoidal, Exponential Association 3, Gaussian, Natural Logarithm and Reciprocal Quadratic YD were the most important models. The hornbeam species follows different models at different altitudes and aspects (except in the northeast aspect which only showed a Rational Model at different altitudes). Nonlinear Regression Models performed reasonable in showing the relationship between tree characteristics including diameter-basal area and diameter-canopy cover. It is recommended to use such models for other species in the region with environmental factors to provide complementary results for more accurate management guidelines.