Diameter distribution models of selected tropical tree species in the University of Ibadan, Oyo State, were modelled with four probability density functions which are Weibull, Burr, Log-Logistics and Gamma distribution. Two study sites were selected within the University for assessment which are; Heritage park and the Teak plantation. The Heritage Park consists of Terminalia radii species plantation while the Teak plantation consists of Tectona grandis species. Total enumeration of the Terminalia species in the plantation was assessed while in the Teak plantation two (2) transect lines of 150m were established at a spacing of 70 meters apart. Five (5) sample plots of 20m × 20m were set alternately on each transect line at 10m interval and thus summing up to 10 sample plots in the study location. For each study location, all living trees with diameter at breast height (dbh) ≥ 10 cm were enumerated and measured. Data were analyzed using maximum likelihood estimation (MLE) method which was used to estimate the parameters of the probability density function (PDF). To test for goodness of fit of the distribution functions, Kolmogorov-Smirnov (K-S), Chi-squared and Anderson-Darling (A-D) test were adopted to fit the diameter data. The maximum dbh observed for Heritage Park and the Teak plantation were 58.4 cm and 65.8 cm, respectively. Higher proportion of trees falls in the diameter classes of 30 – 39 for both plantations. The result shows that the Weibull distribution and Gamma distribution were the most suitable distributions based on the smallest relative rank sum of 3.69 and 3.21 respectively for each of the locations.
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