Sustainability of intensive loblolly pine plantation management in the South Carolina Coastal Plain, USA

Abstract

There is concern that repeated rotations of intensive loblolly pine plantation silviculture may degrade site fertility and thus not be sustainable. This study was conducted to estimate biomass, N, and P pools in two loblolly pine plantations before harvest and 10 growing seasons after plantation re-establishment. The soil, litter layer, herb layer, and planted loblolly pine trees were sampled then clear-cut harvested and a second rotation plantation established by chemical and mechanical site preparation. These same components were sampled after the tenth growing season, which is 50% of the first rotation for one plantation and 59% for the other. Second rotation soil N pools ranged from 3134 to 5148 kg ha −1, soil P pools ranged from 578 to 767 kg ha −1, and these were equal to or significantly greater than those of the first rotation. Litter layer N and P pools in the second rotation were the same as or significantly less than those of the first. In one plantation the litter layer N pools were 21–35% of the first rotation and 67–82% in the other stand. The greatest change was in the herb layer with one second-rotation plantation developing an herb layer biomass 6–32 times that of the first rotation. The other plantation had up to an eight-fold increase in the second rotation herb layer biomass compared to the herb layer of the first rotation plantation. Tree biomass accumulation was not proportional to age; it was less. However, the tree N and P pools were equal to or greater than those predicted by age. In one plantation, the tree N pool was 109–223 and 71–207 kg ha −1 in the other plantation. I propose that the best indicator of sustainability is the conservation of site nutrients, in this case, N and P. Both plantations accumulated N and P faster than predicted by age, indicating that these forest management practices not only conserved site nutrients, but also allowed accumulation. These practices are sustainable by this measure.