SUITABILITY OF THE NORMAL, LOG-NORMAL AND WEIBULL DISTRIBUTIONS FOR MODELING DIAMETER AND HEIGHT DISTRIBUTIONS OF Swietenia mahagoni PLANTATIONS IN BANGLADESH

The diameter and height distribution of the growing stock is an essential starting point in many forest management planning problems. There are several methods for predicting the diameter and height distribution of a stand, varying from methods which utilize theoretical distribution functions to non-parametric methods. Data from 160 plots, established of Swietenia mahagoni L. plantations (sample size – 20 m x 20 m) were stratified by year into eight different ages plantations planted in the north-eastern region of Bangladesh from 1999-2013. The parameters of the Weibull distribution were calculated using maximum likelihood estimation (MLE) and moment estimation (ME) methods. The goodness of fit of normal, lognormal, Weibull MLE and Weibull ME were tested using one-sample Kolmogorov-Smirnov (KS) tests. After that, The MLE and ME of the Weibull distribution was best fit to be suitable and the lognormal distribution was also found as fit for 1 to 7 years of plantations but the normal distribution did not provide a satisfactory description of the data. The results suggest that the Weibull distributions were effective for describing the diameter and height distributions which derived were statistically and biologically acceptable and could be satisfactorily used for stands of Mahagony plantations grown in Bangladesh.