Are intensive pine plantation establishment practices sustainable? An assessment of soil carbon and nitrogen in successive loblolly pine (Pinus taeda L) plantations in the southeastern United States

The sustainability of plantation forestry is a concern.  Management practices can remove site nutrients which may not be replenished during the short rotations.  A study was established in a loblolly pine (Pinus taeda L.) plantation in North Carolina to determine the impacts of establishment practices on long-term site productivity.  The study was installed as a factorial design with two levels of harvest (whole tree (WT), stem only (SO)), site preparation (shear, pile, and disk (SPD), chop and burn (CB)), and vegetation control (herbicide application (HR), no control (NO)).  Forest floor and mineral soil (0-60cm) carbon (C) and nitrogen (N) assessments were conducted before harvest (1980) and 25 years later (2005), at the end of the 3^rd rotation.  Annual litterfall was measured in 2005.  By 2005, the SPD treatment had resulted in lower soil C and N than CB, and had caused a 10% reduction in soil C between the two rotations.  The WT harvest resulted in a reduction in soil C from 1981-2005 at three soil depths.  In contrast, the CB treatment resulted in an increase in soil C at 10-20cm.  No significant changes in soil N were found between rotations for any of the treatments.  Vegetation control only impacted forest floor, with plots receiving HR having larger amounts of forest floor N and C.  None of the treatments affected annual litterfall.  The results from this study indicate that establishment practices and a 25-year rotation can result in both losses and gains in soil C, but have minimal impacts on soil N.