Fitting diameter distribution for <i>Gmelina arborea</i> (Roxb.) stands in Omo Forest Reserve, South Western Nigeria

Abstract

Effective forest plantation management and decision making can be achieved by applying probability distribution to predict the stand  status in diameter class distribution. The purpose of this study is to develop a suitable diameter distribution model for different age  series of Gmelina arborea plantation stands in Omo Forest Reserves Ijebu East, Ogun State, south-western Nigeria. The Gmelina  plantations were established in 2005, 2008, 2010, 2012 and 2014 respectively. A total of 30 temporary sample plots of equal size (25m x  25m) were laid while complete enumeration was carried out in each sampled plot and tree growth variables such as diameter at breast  height and total height of all trees were measured. Eight diameter distribution functions that rank best includes Gen.Pareto, Beta,  Lognormal (3P), Weibull (3P), Gamma (3P), Exponential (2P), Chi squared and General Extreme Value were fitted and assessed with  Kolmogorov Smirnov (K-S), Anderson Darling and Chi-Square. General Pareto Distribution with D value of 0.04382 was ranked the best  distribution with the Kolmogorov Sminorv test. The positive skewness recorded is an indication that most of the diameter at breast height  are concentrated in the lower diameter class and it is an indication of a healthy and vigour forest.