Improved prediction of hardwood tree biomass derived from wood density estimates and form factors for whole trees

Data from hardwood trees in Michigan were analyzed to investigate how differences in whole-tree form and wood density between trees of different stem diameter relate to residual error in standard-type biomass equations. The results suggested that whole-tree wood density, measured at breast height, explained a significant proportion of residual error in standard-type allometric equations, but whole-tree form factors explained more. However, such form factors are highly variable from tree to tree and may be difficult to predict with any precision from simple tree measurements. Whole-tree form factors were found to be highly correlated with the percentage of total aboveground mass in tree branches, which likely relates to the allometric scaling of the deliquescent hardwood growth form. These results suggest that further studies are needed to understand whole-tree form factors and incorporate them into tree biomass equations.