International Science Community Association Research Journal of Agriculture and Forestry Sciences 14 2 2026 04 8 Development of Yield Function and Height-Diameter Trees Species in Arboretum, University of Port Harcourt, Nigeria 1 8 EN I. Amadi 1 Department of Environmental Forestry and Wildlife Management, University of Port Harcourt, Nigeria A.S. Ogunbode 2 Department of Environmental Forestry and Wildlife Management, University of Port Harcourt, Nigeria > Research Paper 2026 1 23 2026 04 8 The aim of the research was to create models for forecasting tree heights and stem volumes of tree species stands in the Arboretum at the University of Port Harcourt, using simple random sampling. All trees were determined for their diameters at breast height (Dbh) and overall height. The data were examined using descriptive and regression methods. Height-diameter and stem volume models were fitted to the dataset using linear, logarithmic, quadratic, and cubic functions. The analyst was tree Dbh (cm). The established models were evaluated using the coefficient of determination (R2), root mean square error (RMSE), and Akaike's information criterion (AIC). Model justifications were performed using the t-test and mean bias. All the results for the selected models were significant (P <0.05), height-diameter models consistently gave poor outcomes with low R2 values. The best among the height-diameter models is quadratic function with R2; RMSE and AIC values of 0.50; 4.03 and 5787. Also, volume models had very high R2with low RMSE and AIC values among which quadratic modelhad the best with highest R2; RMSE and AIC values of 0.93, 0.44 and 662.1. Model validation in all the height and yield function revealed no significant difference between the observed and the predicted of height and stem (P>0.05).The study recommended linear and quadratic models for trees in the plantation, due to their satisfactory of height and yield prediction as well as strong biological interpretability. Copyright@ International Science Community Association