Modeling loblolly pine plantations across planting densities and management intensities: I. dominant height and site index models

Stand-level growth and yield (G&Y) models are essential for guiding forest management and assessing the effects of silvicultural regimes on volume, biomass, and carbon dynamics. A key component of G&Y systems is the dominant height (HD) model, from which site index (SI) is derived. Although HD has traditionally been assumed to be relatively insensitive to stand density within a moderate range, plantation forests are established across wide ranges of planting densities and are often subject to intensive management, both of which can influence HD development. Using long-term data from loblolly pine culture by density studies spanning broad planting densities and management intensities in the southeastern United States, we developed new HD models that satisfy three desirable properties: base-age invariance, compatibility between prediction and projection formulations, and logical behavior in approximate limits. Asymptotic height varies with inherent site quality, planting density, and management intensity, and the relative HD growth rate at a given age is influenced by management intensity. From these models, we derived both a base SI equation representing inherent site quality and an expressed SI equation reflecting the effects of planting density and management. The expressed SI increased with increasing initial planting density and management intensity. Distinguishing between base and expressed SI, particularly within stand-level G&Y systems, enables clear separation of site quality effects from those of planting density and management practices. • Developed dominant height (HD) models for loblolly pine across planting densities and management intensities. • Models ensure base-age invariance, compatibility, and logical limiting behavior. • Asymptotic HD varies with site quality, planting density, and management intensity. • Relative HD growth rate is influenced by management intensity. • Derived base and expressed site index (SI) equations, with SI increasing under higher density and management intensity.