Modeling Diameter Distribution of the Tropical Rainforest in Oban Forest Reserve

Abstract

Diameter distribution model was developed for tropical rainforest of Oban Forest Reserve. Multistage sampling technique was adopted for the study. The sampling procedure was made up of primary, secondary and tertiary sampling units. A total of 808 trees were measured in 14 tertiary sample plots (40m x 50m). Tree outside bark diameter at breast height (dbh) data, were measured for tree species with dbh ≥ 10 cm within the tertiary sampling units. Data were analysed on several probability density function (pdf), then ranked based on Kolmogorov smirnov, Anderson darling and Chi-Square. The best six distributions (Beta, Burr 4P, Gamma 3P, Johnson S_B, Lognormal and Weibull 3P) were further tested with Kolmogorov smirnov (D) and Chi-Square () for fitting the diameter data. The results indicated that there are more trees in the lower diameter class than the upper diameter class. Weibull 3P and Johnson S_B distribution were adjudged more flexible when tested with Kolmogorov smirnov and Chi-Square respectively. The reason is because their calculated values (Weibull 3P = 0.02397 and Johnson S_B = 3.8161) were the lowest values and less than the tabulated values (D = 0.05 and () df₉ = 16.919 respectively) at p ≥ 0.05. This implies the data followed the specified distribution and that Weibull 3P and Johnson S_B can appropriately provide a better fit for the diameter data in Oban Forest Reserve.