Diameter distribution modeling of Quercus persica using probability distribution functions in open forests (Case study: Dalab of Ilam province)

The diameter at breast height of tree is one of the important characteristics in forest measurements. Diameter structure of forest stands can be determined based on diameter distribution. The distribution of diameter classes is the most important structural characteristics of forest stands. The aim of this study was to evaluate the DBH probability distribution of Quercus persica trees in Dalab open forests of Ilamprovince. For this purpose, 37 transects with fixed length (50 m) were measured and trees distribution in diameter classes for 209 trees were fitted. The probability distribution functions including: Beta, Gamma, Normal and Log-normal were fitted to the DBH distribution of oak trees. The maximum likelihood estimator was used to evaluate the distribution functions parameters. Expected probability and probability derived from functions were compared using Kolmogorov-Smirnov and Chi-square tests. Results of fitting tests and P-P plots showed that Beta and Normal distributions were the best probability for diameter distribution modeling in Dalab open forests of Ilamprovince.