Relationships among Diameter at Breast Height and Loblolly Pine Attributes from Local and Nonlocal Seed Sources near the Western Edge of the Natural Range of Loblolly Pine

Individual loblolly pine sample trees planted in 1983 as part of a seed source and density study on Carter Mountain near Broken Bow, Oklahoma, were used to investigate the effects of seed source and density on the relationships between dbh, height, crown length, and individual tree volume. The study site is a rocky, mountain soil near but outside the western boundary of the loblolly pine natural range in Oklahoma. North Carolina coastal and Oklahoma–Arkansas seed sources were planted at 4 × 4-, 6 × 6-, 8 × 8-, and 10 ×10-ft spacings. Individual tree measurements were available at plantation ages 17, 18, 19, 22, and 25 years. The dbh of sample trees ranged from 4 to 13 in., and heights ranged from approximately 30 to 70 ft. Regression relationships between individual tree dbh and height indicated a significant difference due to seed source, with the North Carolina source being approximately 7% taller across the dbh range in these data. This indicates that the North Carolina seed source is taller for a given dbh even at the extreme western edge of the loblolly natural range. The average dbh-height relationship also was significantly affected by density, but the North Carolina seed source was taller on average per given dbh for all densities. In addition to being taller for a given dbh, the North Carolina had a longer live crown and more cubic stem content than the Oklahoma–Arkansas seed source.