Diameter distribution of Nauclea diderrichii (D Wild) Merr. Plantations in a restricted tropical rainforest of Nigeria

Abstract

Distribution of tree diameter in a specific stand provides basic information for forest management. Little attention is given to the use of probability distribution functions in characterising the stem diameters of most Nigeria indigenous species. This study used Three-parameters lognormal and Weibull probability distribution functions in characterising the diameter of Nauclea diderrichii plantations within a restricted tropical rainforest of Nigeria for sustainable management. Thirty temporary sample plots of dimensions 20 m × 20 m were randomly laid in three age strata (42, 43 and 46 years). Stem diameters of all living Nauclea diderrichii trees with diameter at breast height ≥10.0 cm in all the sampled plots were enumerated. The performance and suitability result revealed that lognormal distribution gave superior description of the stem diameter for the Nauclea diderrichii species in the study area, with least values of Bias (0.00001), Mean absolute error (0.1214), Mean square error (0.7421), Kolmogorov-Smirnov (0.02781) and Anderson Darling (0.49562) statistics. Hence, three-parameter lognormal using maximum likelihood method was recommended for distributing stem diameter of Nauclea diderrichii in the study area.

Keywords: Indigenous species; Lognormal; Maximum likelihood; Probability distribution function; Weibull