Fitting frequency distributions of trees diameter at breast height in different growth stages in Asalem mixed forests of Guilan

The distribution of diameter classes is the most important structural characteristics of forest stands. Determining the fitting pattern of diameter classes in forests shows that, the overall status of these forests from the destruction process and ecological sequence points of view at different times. The aim of this study was to evaluate of frequency distributions of trees DBH in different development stages of natural stands in forests of Guilan. In order to study the statistical distributions of trees dbh,In order to determine the mixed stands characteristics in untouched forests for applying in silvicultural interventions, a reserve area in region in watershed number 9 (shafarod) from west of the Hyrcanian forests, northern Iran was selected. three sample plots of one hectare, were selected in three development stages. In three of development stages initial, optimal and decay were measured 419, 259 and 161 trees respectively. Beta, gamma, normal, lognormal, exponential, logistic and Johnson’s SB probability distribution patterns were fitted to diameter classes. Characteristics of distribution patterns were estimated using maximum likelihood method. Kolmogorov-Smirnov, Anderson-Darling and Chi-square tests were used for comparing of actual probability and probability which derived from functions. The results showed that the proper distribution function is different in three stages; So that in the initial stage, Johnson’s SB, in optimal stage, the Weibull, and in the decay stage, Weibol and Johnson’s SB have a good fit. Therefore, these distribution functions can be used for those who want to simulate changes of forests.