Evaluation of probability distribution functions for fitting stem diameters of Tectona grandis plantation in Adekunle Ajasin University, Ondo State, Nigeria

Modeling frequency distributions of tree variables, such as Diameter at Breast Height (DBH) plays an important role in forest inventories, growth prediction, and management. The objective of the study was to evaluate the 2 and 3-parameters Gamma, Log logistics, Lognormal and Weibull, distribution functions fitted to the DBH of Teak (Tectona grandis Linn. F.) plantation in Adekunle Ajasin University, Akungba Akoko, Ondo State, Nigeria for sustainable management. The method adopted for this research was complete enumeration of the Teak plantation of size 80 m2 x 40 m2. The performance of the selected probability distribution functions (PDFs) was compared using Kolmogorov-Smirnov (K-S), Anderson-Darling (A-D) and Chi-square (ꭓ2) tests. The results showed that the highest frequency (526) of trees fall between the DBH of 0.11-0.14 m. The Weibull 3-parameter distribution had the best fit with K-S= 0.0222, A-D= 0.3908 and ꭓ2=10.868 and followed by Weibull 2-parameter distribution with K-S= 0.0238, A-D= 0.4944 and ꭓ2=10.443. Hence, Weibull 3 and 2-parameters were adjudged as the most suitable distribution also based on the smallest relative rank sum of 17 and 27, respectively in the study area. The study recommends the Weibull 3-parameter for DBH class distribution of the Tectona grandis plantation in the study area for plausible management and value projection.