Prediction of individual tree seedling volume, biomass, and carbon content via allometric projection

When making assessments of forest resources, there is nearly ubiquitous interest in quantifying current status and trends in tree biomass and carbon stocks. While important at various spatial scales, typical estimations pertinent to broad forest management and policy issues are conducted for large areas such as state, regional, and national perspectives. These assessments are usually accomplished using large-area forest inventory data collected by National Forest Inventory (NFI) programs. While NFI efforts commonly collect size data for individual trees, there is often limited information for tree seedlings, e.g., frequency by species. To fully describe the tree population across the entire range of sizes present, this study proposes methods to predict individual seedling groundline diameter and height using models developed from trees having a diameter at breast height (DBH) less than 7.62 ​cm. These attributes are subsequently used for the prediction of seedling stem volume, total aboveground biomass, and carbon content. The results suggest a smooth transition in tree attributes as size increases to where direct measurement of individual trees and prediction of their volume, biomass, and carbon are implemented as part of standard inventory protocols. Analyses including the full spectrum of tree sizes show that seedlings contribute roughly 0.6%–0.7% of the total tree volume/mass. This additional suite of information provides opportunities for more holistic assessments across the full spectrum of the tree resource or for specialized subdomains that include the seedling component.