Variation of the Form Factor of Terminalia alata in the Chure–Terai Region, Nepal

Accurate estimation of tree volume is crucial for informed decision‐making in forest management. The form factor (FF), which adjusts the volume of a cylinder to match the true shape of a tree, plays an essential role in this estimation process. Current practices in Nepal use a uniform FF of 0.5 for all tree species and sizes, resulting in inaccuracies. This study investigates the variation in the FF with size (diameter at breast height [DBH]) of Terminalia alata , an important timber species in Nepal’s Chure–Terai regions. The specific objectives were to estimate the average FF for different DBH classes, analyze the correlation between DBH, height, and FF, and recommend a model to predict FF from these variables. This study utilized data retrieved from the Forest Research and Training Centre (FRTC)’s archive, involving destructive sampling of 58 trees. The volumes of the tree sections were calculated using the cone formula for the top section, Smalian’s formula for the middle sections, and the cylinder formula for the base section. The average over‐bark and under‐bark FFs were found to be 0.41 and 0.4, respectively. Significant variations in FF across DBH classes were observed for both over‐bark and under‐bark measurements. The Pearson correlation test confirmed a significant relationship between FF, DBH, and height, with FF decreasing as DBH ( r = −0.610) and height ( r = −0.604) increase. A quadratic model, FF(Ob) = 0.5056 − 0.003141 DBH(Ob) + 0.00001462 DBH(Ob) 2 , was identified as the best fit (Adj. R 2 = 0.40, RMSE = 0.049) for estimating the FF. This study suggests that using FFs specific to different DBH classes will improve the accuracy of tree volume estimations.