Floristic Composition and Diameter Distribution Models for The Management of Omo Biosphere Reserve, Ogun State, Nigeria

Abstract

Stem diameter distributions is highly needed in majority of forest management decisions. This study developed some models for describing the diameter distribution of Omo Biosphere Reserve in lowland rainforest ecosystem, Nigeria. Systematic sampling design was used to lay three straight line transects, four temporary plots of 0.25ha (50 m x 50 m) were laid in alternating position along each transect at 100 m interval to make up a total of 12 plots for the study and Diameter at breast height (DBH) was measured for all trees with Dbh ≥ 10cm in every plot. A total of fifty-seven species were encountered and exploratory analysis of the collected data showed that the observation was right skewed consequently resulting in the choice of six probability diameter distributions functions using Maximum likelihood estimator. The selected distribution models are Weibull, Lognormal Distribution (LN), Gamma, Logit-logistic (LL) and Burr distribution. The Kurtosis and Skewness are 6.43 and 1.34 respectively with a mean Dbh of 36.40cm. Burr had the least values of Kolmogorov Smirnov (Dn) (0.046), Anderson Darling (AD) (1.102) and Cramer-von Mises (CvM) (0.178). This is followed by log logistic with 0.05, 2.769 are 0.258 for Dn, AD and CvM respectively. High and positive skewness and kurtosis values reflect abundance of trees in the lower Dbh class. These are sufficient to replace the trees in the upper dbh class through regeneration. Hence, the Burr and Log-logistic distributions were adjudged the most flexible to describe the diameter structure of Omo Biosphere Reserve.