Size Heterogeneity and Growth Dominance Development in Unthinned Loblolly Pine Plantations under Contrasting Management Intensities

Understanding how management alters stand structural development is essential for improving loblolly pine (Pinus taeda L.) plantation productivity. Although intensive management increases productivity, its effects on tree size inequality and size–growth relationships remain poorly understood. We compared structural characteristics between extensively and intensively managed plantations in the western Gulf Plain, USA. Gini indices (GI) and growth dominance (GD) were calculated for diameter at breast height (DBH) and height. Generalized additive mixed models assessed effects of stand age, site index (SI), and stand density index (SDI). Intensively managed plantations exhibited lower inequality in DBH and height than extensively managed plantations, whereas management had little effect on relationships between GI and stand age, SI, and SDI. GD differed markedly between management regimes. DBH GD shifted from negative to weakly positive during stand development, indicating a transition from small-tree growth advantage to asymmetric competition. Intensive management accelerated this transition, shortening its duration. Height GD remained negative throughout development, indicating persistent growth advantage of shorter trees, although intensive management altered its temporal pattern. GI was significantly associated with GD, but relationships differed between DBH and height and explained little variation. Overall, intensive management alters stand structural development and competitive dynamics in loblolly pine plantations.