Equations for Estimating Biomass, Foliage Area, and Sapwood of Small Trees in the Southern Appalachians

Small trees and shrubs play an important role in forest diversity and regeneration and may contribute substantially to ecosystem fluxes of carbon and water; however, relatively little attention is given to quantifying the contribution of small trees to forest processes. One reason for this may be that the allometric equations developed for large trees tend to systematically underestimate structural variables such as biomass and foliage area when applied to small trees, both on an individual tree level and at the stand level. To test this hypothesis, we developed allometric equations for trees 10 cm dbh (D) for seven dependent variables (woody, foliage, and total biomass; woody, foliage, and whole-plant surface area; and sapwood area) and compared these new equations with the existing equations for large trees. We found significant differences between small tree and large tree equations for most variables and showed that equations for large trees tend to underestimate the structural characteristics of small trees. When we applied new size-specific equations to forest survey data representing a chronosequence of forest development, estimates of small tree biomass increased 30–73% and estimates of foliage area increased 72–142% compared with results using only equations for large trees. These results suggest that small trees can contribute substantially to forest structure and associated ecosystem fluxes, especially in stands with a large proportion of small trees. However, size-specific equations for small trees did not substantially change the estimates of forest biomass in these stands, and the need to develop size-specific equations may depend on the variables of interest.