From volume to surface area: A compatible stem surface area equation

Stem surface area plays a key role in stem respiration, methane exchange, tree growth, and rainfall interception, and as a habitat for diverse organisms. However, methods for estimating stem surface area remain limited compared with well-established stem volume equations. In this study, a compatible equation for predicting stem surface area that shares coefficients with existing volume equations was developed. The equation was derived based on the square root law of form-factors and requires diameter at breast height, tree height, and a taper index based on form-factors (TIFF). Its validity was tested using empirical data from <i>Pinus banksiana</i>. No significant difference was found between the predicted and observed stem surface areas, with a relative mean bias of −0.063% and a relative root mean square error of 5.493%. TIFF variability is expected to have a limited effect on surface area estimates. This insensitivity enables extensive forest inventory data, including diameter at breast height and tree height from continuous and national forest inventories, to be applied immediately without the need for supplementary field measurements. The equation provides a practical pathway to shift from volume-based forest mensuration to a surface-area-based quantification of land–atmosphere exchange processes.