Estimating Long-Term Carbon Sequestration Patterns in Even- and Uneven-Aged Southern Pine Stands

Carbon (C) sequestration has become an increasingly important consideration for forest management in North America, and has particular potential in pine-dominated forests of the southern United States. Using existing literature on plantations and long-term studies of naturally regenerated loblolly (Pinus taeda) and shortleaf (Pinus echinata) pine-dominated stands on the Crossett Experimental Forest, allometric biomass equations, and reasonable assumptions about forest product life cycles, we projected the net C pools of the following silvicultural systems over a 100-year period: a short rotation loblolly pine plantation (4 rotations); a seed treebased (natural origin) even-aged loblolly/shortleaf pine stand (2 rotations); and an uneven-aged loblolly/shortleaf pine stand (20 cutting-cycle harvests under the selection method). Both the seed tree stand and the intensively managed pine plantation produced large (if fluctuating) quantities (up to almost 190 tons/ha) of aboveground live biomass. Though not as productive as the even-aged treatments, the uneven-aged pine stands produced a steady stream of sequestered C in the form of high quality sawtimber while simultaneously maintaining a steady stock of 61.5 to 78.5 tons/ha of live aboveground biomass. Belowground C sequestration was also substantial in uneven-aged stands, with a fairly constant 13.3 to 16.9 tons/ha of coarse roots in the standing live pine crop. While shorter rotation even-aged stands tend to produce smaller coarse roots, their higher stocking levels more than offset this, and hence these stands have more live belowground biomass during most of the rotation (up to almost 41 tons/ha). By the end of the 100-year simulation, the even-aged stands had sequestered approximately 120 tons/ha of C in live tree and product pools, or about 50 percent more than the uneven-aged stand. The uneven-aged stand, however, maintained a more stable residual live tree C store, and fluctuated (only ± 2 tons/ha/yr) far less than either even-aged treatment. Averaged over the period, annual C storage ranged from 0.38 to 1.11 to 1.16 tons/ha for the uneven-aged, seed tree, and plantation, respectively. Though it is difficult to compare these values to other simulations, the data show that managing loblolly pine stands is an effective way to sequester C, even if their patterns differ appreciably.