Implementing regional locale and thinning response in the loblolly pine height-diameter relationship

This study uses two regionwide data sets, one exemplified by intensive management and the other by nonintensive management, to investigate whether including regional locale and thinning response improves the loblolly pine height- diameter relationship. Results showed that including geographic coordinates as scaled variables, in addition to including a thinning response modifier, reduces the variability of an individual-tree height model compared with a baseline model without these covariates. Holding stand conditions constant, tree height for a given diameter will generally be greater at south and east locales within the natural range of loblolly pine, and thinning will lead to slightly greater tree heights. Equations that include geographic locale of the stand and a thinning modifier that incorporates amount of time since thinning are proposed. These equations can be used for thinned or nonthinned stands throughout the natural geographic range of the species.