Parameters of the Weibull diameter distribution were estimated for Gmelina (Gmelina arborea) plantation in Nimbia Forest Reserve. Stratified random sampling was employed to select five plots of 20 × 20 m from each forest bit that serves as management unit, thereby having a total of 20 plots for the study. Stump diameter (Dst), diameter at breast height (Dbh), diameter at middle and top positions (Dm and Dt) of trees, and tree height for all the selected trees were measured. Average Dbh measured was 16.33 cm and the mean tree height 6.85 m. Pseudo coefficient of determination (Pseudo R2), residual mean square error, Anderson-Darling, and Kolmogorov-Smirnov goodness-of-fit statistics were considered as model selection criteria. Weibull cumulative density function (Weibull-CDF) was the best fit method for Gmelina compared with the Weibull probability density function based on the goodness-of-fit statistics generated. The diameter distribution models produced are considered only efficient for tree stands of seven years rotation age, while additional site factors like spacing, density and silvicultural treatments are required for better models, hence the need for establishing permanent sample plots (PSP) in order to get additional information from re-measurements of the plots.
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