effects of three different silvicultural systems on diameter distribution in shafaroud forest stands of iran

the implementation of different silvicultural systems can be effective on different characteristics of forest stands, such as stand structure and diameter distribution of trees. this study was carried out in shafaroud forests of gilan province of northern iran. the objectives of this research were 1) to evaluate the suitability of different probability distribution functions, including weibull, beta, gamma, johnson, lognormal, normal and exponential, for modeling tree distribution in diameter classes and, 2) to compare changes of diameter distributions after ten years of implementation of three different silvicultural systems. the tested systems were single-tree selection, shelterwood and strip cutting. also, there was an untreated stand. the results of chi-square and kolmogorov-smirnov tests showed that the johnson, gamma and lognormal models were often more flexible to fit various diameter distributions, while in any case, the beta and exponential probability distribution did not provide satisfactory descriptions of the experimental data. other results indicated the change in the diameter distribution due to the implementation of the strip management system, a decade after timber harvest. this may mean that strip cutting can disturb the stand structure in the studied forests. also, there were no significant changes in the diameter distributions after implementation of the other silvicultural systems.