Individual tree basal area equation for a young Tectona Grandis (Teak) plantation in Choba, Port Harcourt, Rivers State, Nigeria

An individual Tree Basal Area Equation was developed for a Young Tectona grandis plantation of the Department of Forestry and Wildlife Management, Faculty of Agriculture, University of Port Harcourt (UNIPORT) Choba, Rivers State; using diameter at breast height (dbh), diameter at the base (db), crown diameter (CD), and crown projection area (CPA) as predictor variables. The individual basal area estimates were obtained from data collected from 437 trees in the five-year-old plantation of dimensional area of 2737.5m2.The individual trees were measured for dbh, CD, and db using traditional measuring techniques, while individual Basal Area (BA) and CPA were estimated from the data sets. The data collected were further subjected to descriptive, correlation and regression analyses with different empirical models, using STATISTICA statistical package. The results of the descriptive analyses produced a mean values of DBH of 7.89±0.0097 cm, BA with the mean value of 0.0052±0.0001 m2, DB with 32.64±0.397 cm, CD of 3.1004±0.041 m and CPA with a mean value of 8.1268±0.215 m2. The results of regression analyses and modelling with empirical non-linear basal area equations fitted with Quadratic models, Exponential models, Linear Fit models and Polynomial models on STATISTICA produced best fits estimates in accordance with residual analyses and fit indices such as Mean Prediction Residual (MPR), Standard Error of Estimate (SEE), Residual Coefficient Variation (RCV) and Prediction Sum of Squares (PRESS). The Quadratic equation (BA = bo + biCPA + DB2; R2 - 0.8959; SEE - 0.0004) after the evaluation procedures gave the most robust fit indices for the individual basal area, and was thus adjudged the best individual basal area equation for Tectona grandis plantations in the study area. This study has shown that the selected model can be effectively used for predicting individual tree basal area of Tectona grandis both within the study area and in any other Tectona grandis plantations and, hence, for management and for making timber harvest decisions.