Loblolly pine outperforms slash pine in the southeastern United States – A long-term experimental comparison study

Abstract

Loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.) are the two most important commercial timber species in the southeastern U.S. A long-term experimental comparison study, in which loblolly and slash pine plots were paired for combinations of planting density (741, 2224, 3706 trees ha−1) and cultural intensity (operational versus intensive), was established in the lower Coastal Plain to investigate species differences in growth dynamics. Using age 2–21-year inventory plot data and destructive biomass/nutrient sampling data, species comparisons were conducted comprehensively, and the reasons of the species differences and management implications were discussed. When compared to slash pine, loblolly pine had higher stand basal area carrying capacity and maximum stand density index, lower fusiform rust infection rate and less wind damage, leading to its lower mortality. With no species difference in average DBH, loblolly pine consistently had greater average height and live crown length and higher level of tree size inequality. Loblolly pine had lower foliar biomass and lower foliar density, and higher crown length/width ratios due primarily to its longer crowns, suggesting perhaps a slightly greater shade tolerance or less dense canopy. As a result, loblolly pine outperformed slash pine in terms of stand basal area, total volume, aboveground biomass and carbon accumulation. Loblolly pine consistently accumulated more potassium, and this species difference increased with increasing stand age; while slash pine had slightly higher nitrogen and phosphorus contents before age 12. Species differences in mortality patterns and in nutrient accumulations in aboveground biomass emphasized the need to develop species-specific management strategies including different thinning and fertilization regimes.