Study of Effective Factors on Diameter increment and Mortality of Individual trees in uneven-aged stand

Today, the important of growth models as an important management tool and factors affecting them is clear. So, in this study, factors affecting the growth models were examined. Data from 256 permanent sample plots for the years 2003 and 2012 of Kheyroud Forest was used. First, the relationship between topographic factors including slope, direction and altitude with site productivity for beech was obtained using an empirical regression model. Then, the factors affecting the individual trees diameter increment were investigated using regression relations. Also, in order to better understand the effect of these factors, tree species were separated in four species group as beech, hornbeam, chestnut-leaved oak and other species. In order to evaluate the model, three statistics including RMSE, MBE and performance coefficients were used. The results showed that the relationship between the site productivity index and three factors of direction, gradient and elevation is sinusoidal, almost decreasing, at first increased and then decreased. Also, the behavior of the studied indicators in relation to tree species is different. For instance, in the diameter increment model of beech species, all of the indices, except for site productivity and Shannon-Wiener index had a significant effect and the use of these indicators for beech species reduces the error and bias and increases the efficiency of the model. The mortality model was also presented with a high percentage prediction. In general, the present study showed that the relationship between growth models and various indices has a lot of complexity and more research is needed.