Family and spacing affect stem profile of loblolly pine at age 19

Profile measurements were taken on a stratified sample of 19-year-old trees from 8 North Carolina families and a commercial Mississippi-Alabama check established at 3 spacings (5 x 5, 8 x 8, and 10 x 10 feet). Measurements were first fitted on a single profile equation using multiple-regression. Data were also segregated by family, spacing, and family-byspacing and fitted on the equation. These new model types were tested using the reduction-sum-of-squares principle. Stem volumes were calculated using the different model types and compared. A significant decrease of error was obtained from the reduction-sum-of-squares method, indicating that accuracy of stem-volume estimation can be increased by accounting for family and spacing in the profile equation.