Fifty Years of Forest Carbon Budgets at the Calhoun Experimental Forest.

During the first 30 to 40 years of pine forest development on old cotton fields in the South Carolina piedmont, a rapid accumulation of carbon in tree biomass dominated the ecosystem carbon budget of the Calhoun Experimental Forest. The O-horizon and surficial mineral soils (0-15 cm) also accumulated carbon rapidly, while the carbon content of deeper soils (35-60 cm) steadily declined. Now, after 50 years of forest development, a large fraction of the original pines have died and fallen to the ground, and thus the forest is accruing large amounts of carbon in coarse woody debris in logs and stumps atop the soil surface and in dead roots beneath. Surficial soil layers have continued their rapid carbon accumulation, while deeper soils show no sign of increase. Additionally, part of the experimental forest has been recently clear-cut, resetting the process of ecosystem succession and carbon accumulation. Here we present an updated carbon budget of the fifty-year-old Calhoun Experimental Forest, including previously-unsampled, slowly-cycling pools such as above- and below-ground coarse woody debris. Additionally, we have attempted to quantify and predict net carbon sequestration in the Calhoun Forest before and after an operational clear-cut harvest of half of the long-term plots. We intend to use these findings to inform management of Southeastern pine forests for both wood products and carbon storage.