Characterization of diameter distribution data in near-natural forests using the Birnbaum–Saunders distribution

Abstract

The purpose of this study is to investigate the suitability of the Birnbaum–Saunders distribution to model diameter at breast height (DBH) distributions of near-natural complex structure silver fir ( Abies alba Mill.) – European beech ( Fagus sylvatica L.) forests. The investigations were carried out in Świętokrzyski National Park, situated in Central Poland. To estimate the parameters of the Birnbaum–Saunders distribution, three methods were used: the maximum likelihood method (MLE) and the mean–mean estimator, the modified moment method (MME), and the graphical method (GME). The empirical DBH distributions in near-natural fir–beech stands, which arose according to the model taking into account the overlapping of fir mortality and beech regeneration, were generally conformed to the Birnbaum–Saunders distribution. In such forests, the Birnbaum–Saunders distribution approximated the empirical DBH distributions more precisely than the Weibull and gamma distributions.