Analyzing the Diameter Distribution of Juniperus excelsa M. Bieb Stands of Northeast Iran, Using Probability Distribution Functions

Aim: the present study aimed to analyze the diameter distribution of Juniperus excelsa m.bieb stands of northeast Iran, using probability distribution functions consider to cardinal directions. Materials & Methods: The data have been collected from ۱۶۸ sample plots of ۰.۱ha areas in natural juniper stands of Iran. In this study, the diameter distribution of the juniper stands has been evaluated in four main geographical aspects, using various statistical distributions. Weibull (two- and three-parameter), Gamma (two- and three-parameter), Beta, Johnson, and lognormal probability distributions have been used for modeling diameter distribution. Findings: According to the Kolmogorov-Smirnov test, the most appropriate distribution functions in the northern, eastern, and southern slopes were the two-parameter Weibull and Johnson probability distributions western slopes, the most appropriate distribution functions were Beta and Johnson. Besides, considering Anderson-Darling’s fitting test, only lognormal distribution in the northern, eastern, and southern aspects, and lognormal and three-parameter Weibull in western aspect did not show a significant difference compared with the frequency of trees in diameter classes. Conclusion: Generally, the results show Weibull (۲p) and longermal are the most appropriate statistical distribution functions for describing the distribution of trees in the diameter classes of Juniperus excelsa in different aspects.