Development of Height Equations for Teak (Tectona grandis L.f.) Plantation in Ketou Commune, Ketou, Republic of Benin

Abstract

Aim: To develop Height equation for a seven years old Teak (Tectona grandis) plantation in Ketou commune, Republic of Benin. Study Design: Simple random sampling technique was adopted for this study, in which, 25 plots of 20 x 20 m in size. Information was collected on the species tree height (TH) and Diameter at breast height (Dbh) at 1.3 m above the ground level on a randomly laid 25 plots of 20 x 20 m in size in the entire plantation. Place and Duration: The study was carried out in a private Teak plantation in Ketou commune, Republic of Benin from October to December. 2021. Methodology: The collected data was splitted into two parts: 1,552 trees were used for model development while the remaining 754 was used for data validation. Linear, semi-log, double and exponential equations were fitted to the calibrated tree height data, using stepwise regression method procedures in Statistical Package for Social Scientist (SPSS, version 20). Results: The result revealed that, TH, Dbh and basal area (BA) of ranges between 2.4 – 16.3 m, 5.0 – 16.0 cm and 1.6 x 10-3 to 5.9 x 10-3 m2 respectively for both the calibrated and validated data set. Out of the total number of trees enumerated, only two diameter (dbh) class of 5 – 10 and 11 -15 cm was observed in the plantation. 270 trees (11.7 %) of the trees fell into lower diameter class of 5 to 10 cm, while 2,036 trees (88.3 %) fell into 11 to 15 cm class indicating that the most the tree species are still in pole stage. Correlation analysis between the dependent and independent variables were evaluated. A moderately negative correlation was exhibited with the weighted diameter at breast height. Considerable differences were found among the predictive ability of the selected models. The adjusted coefficient of determination values ranges between 55.5 and 96.7%, while the root mean square error and bias ranges between 0.026 to 1.638 and 1.2 x 10-3 to 5.6 x 10-3 respectively. Judging by the regression analysis criteria’s, Model III gave the highest R2Adj and lowest RMSE value among the competing models. The findings clearly shows that, Model III was the appropriate function to fits the data and was selected as the best equation for describing total height growth of Tectona grandis in Ketou commune, Republic of Benin.