Development of stem volume equations for forest trees on farmlands in south-western Nigeria

Accurate tree volume estimation is crucial for forestry management, particularly in quantifying timber value, planning harvests, and ensuring profitability. However, information on stem volume quantification for trees on agricultural farmlands in Ogun State, South-Western region of Nigeria, is limited. The aim of this study was to develop volume equation for estimating merchantable volume of farmland forest trees in the study area. A complete enumeration of 717 timber trees was conducted on randomly selected farmlands and key growth variables, such as merchantable height and diameter at breast height (Dbh) for trees with Dbh ≥10 centimeters, were measured. Linear and multiple linear regression analyses were performed on the data collected using Statgraphics Centurion software. Eight regression equations were developed and their reliability for predicting tree volume was assessed. The most suitable model chosen was Ln (Vol) = -8.41 + 1.56(LnDBH) + 0.14(Mht), with an R² of 98.54% with Mean Absolute Error (MAE) of 0.07. This volume equation effectively captures the relationship between tree volume, diameter at the breast height and mean height, with high explanatory power and accurate predictions. The model is therefore recommended for volume estimation of farmland forest trees in the study area.