An Appropriate Model for Distribution of Diameter Classes of Natural Beech Stands in the Sangdeh & Shastkolateh Forests

This study has been carried out to obtain an appropriate model for the distribution of natural beech
population in diameter classes'in two different forest areas of Sangdeh and Shastkolateh in nothern Iran.
Two different regions of beech forest were selected according to their varied age as well as varied
growing conditions. These were separated from other sections and therefore four sample areas in one
hectare selected for an overall sampling.Then, the numbers of points were plotted according to diameter
class. Among different variants, diameter at breast height was shown to represent a reasonable
distribution of points. Also statistical distribution of Beta, Weibule, Exponential, and Power were
investigated in relation to distribution of points, their efficiency being concluded through chi-square.
The results indicate that •from among different methods, regression model bears the most suitable
estimation for the mentioned regions. Power model for both selected areas and Beta distribution for
Shastkolateh are expected to end up with reasonable results. Finally it can be concluded, although
selective method is used as an approach ifor the distribution trend in forest stands, but, the above
mentioned models can be recommended as more appropriate for the study areas.