Projecting Carbon Pools in Aboveground Woody Accumulations and Harvested Wood in Loblolly Pine Plantations of the Southern United States: From Stand-level to Regional Scales
Accounting for in-woods carbon storage in carbon accounting systems may be insufficient when substantial amounts of sequestered carbon are harvested and converted to long-lived wood products and landfills. The potential for offsetting greenhouse gas (GHG) emissions by storing carbon in managed loblolly pine forests in the southern United States was projected over the next half-century, both in terms of in-woods aboveground carbon pools and harvested products, including wood used for energy production. A region-wide data set from the Forest Inventory Analysis (FIA) program of USDA Forest Service was used to set initial conditions and estimate model parameters for projecting management activities including plantation area, age distributions of thinning, and clearcut harvest on an annual timestep. The stand-level growth and yield model FASTLOB was linked to the FIA data to project growth rates and annual harvest volumes of sawtimber and pulpwood for the projection period, accounting for annual timber harvests and the life cycles of wood products. In addition to baseline management practices, projections were made for scenarios that assumed increasing management intensities including the use of chemical fertilizers and herbicides and genetically-improved growing stock. Present-day carbon storage in well-managed southern pine plantations averaged 30.54 Mgâ ha⁻¹ (± 2.54%) for aboveground carbon. Over a 50-year projection, annual wood production was 62.1 and 45.9 million green metric tons from pulpwood and sawtimber yield, with roughly one-fourth of the green weight being carbon. Baseline projections showed aboveground carbon pools of up to 341 million metric tons being maintained over the next 50 years, with 93% in aboveground live trees and 7% in coarse woody debris (CWD). The carbon storage in wood products increased steadily over the half-century projection and showed no sign of leveling off, while the storage in plantations was found to remain constant or increase slightly over time. An additional 11 million metric tons of harvested carbon was used for energy per year on average, equivalent to 25% of annual forest-products-industry renewable energy use in U.S.A. Intensified forest management practices showed the potential to increase as much as 30% total carbon stored in in-woods and harvested-wood-products pools, with potential increases up to 40% in energy offsets above the baseline scenario. Reducing management intensity greatly increased in-woods carbon storage potential, but eliminated the wood-products carbon sink.