Form Factor Variability in Khaya grandifoliola Trees in Brazil: Implications for Accurate Volume Estimation

Form factor is a key parameter for describing tree taper and provides a simple yet effective method for estimating wood volume. However, applying a single form factor across all tree sizes and ages may lead to substantial errors in volume estimation. This study aimed to determine form factors and their ability to estimate the wood volume of Khaya grandifoliola trees across a wide range of ages (1 to 18 years) and diameters at breast height (2 to 92 cm). Using an electronic dendrometer, a total of 733 trees were scaled across Brazil to derive total and stem form factors. Wood volume was computed using Smalian’s formula, and form factors were determined and stratified for 10 diameter and 7 age classes. The form factor values ranged from 0.30 to 1.75. Mean total and stem form factors were 0.42 and 0.83, respectively, when grouped by diameter class, and increased to 0.50 and 0.93 when grouped by age class. Results revealed a consistent decrease in form factor with increasing diameter and age, indicating a gradual change in tree shape as trees mature. These findings highlight that using diameter-class specific form factors enhances the accuracy of volume estimation while maintaining the easiness of traditional methods.