NON-LINEAR HEIGHT MODELS FOR MIXED TREE SPECIES IN TROPICAL RAINFOREST OF OKOMU FOREST RESERVE, NIGERIA

Models are essential tools for effective forest management. Tree height-diameter models are used for the management of stand structure in forest plantations. The heterogeneity in species composition and structure of tropical forests constitutes a major challenge in developing height models, especially in Okomu Forest Reserve (OFR), Nigeria. There is inadequate information on height models’ application in Nigeria for most natural forests. Hence, tree height models were developed for rainforest of OFR, Nigeria. Using a systematic sampling technique, 2949 tree species with Diameter at Breast Height ≥ 10 cm found within 60 plots of 50 m × 50 m alternately laid at 200 m intervals on 15 transects (one kilometer each) were identified to species level and enumerated. Eighty-seven tree species were identified. Following standard procedure, cluster analysis was used to classify the trees into 5 species groups (SG 1-5). Data were analysed using non-linear regression at α0.05. Ordinary Least square (OLS) modelling technique was used in fitting the height model for each SG. The best fitted height models were evaluated based on the lowest Standard Error of Estimation (SEE), Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC). The results revealed that Gompertz model performed best for SG 1 with lowest values of SEE (5.12), AIC (2197.52), and BIC (2211.05), SG 2 with SEE (5.53), (AIC) 3514.14, and BIC (3528.94) and SG 5 with SEE (5.30), AIC (2526.19) and BIC (2540.07); while power model performed best for SG 2 with the lowest SEE (3.75), AIC (524.38) and BIC (530.95) and SG 4 with lowest SEE (5.09), AIC (980.38) and BIC (987.79) respectively. This study concluded that total height of mixed tree species in each SG in OFR, Nigeria can be determined with these models. Thus, these models are recommended for modelling height-diameter relationships of mixed tree species in tropical rainforest.