Northeastern States

S2Describes a species-specific, distance-independent individual-tree diameter growth model for the Northeastern United States. Diameter growth is predicted in two steps using a two parameter, sigmoidal growth function modified by a one parameter exponential decay function with species-specific coefficients. Coefficients are presented for 28 species groups. The model accounts for variability in annual diameter growth due to species, tree size, site quality, and the tree's competitive position within the stand. Model performance is evaluated using the mean predicted error and the root mean square error. Results are presented for the calibration data and an independent validation data set. The model has been, incorporated into NE-TWIGS, a computerized forest growth model for the Northeastern United States.S3.