Potential Carbon Sequestration by Afforestation of Pasture in the South‐Central United States

Abstract

AbstractClimate models indicate that increasing atmospheric concentrations of CO2 and other greenhouse gases could alter climate globally. The Climate Change Action Plan commits the USA to reducing net greenhouse gas emissions by 106 ✕ 106 Mg C yr−1 by the year 2000. One suggestion for reducing net emissions is to convert marginal grass pastures to pine (Pinus spp.) plantations in the South‐Central USA. We used the Erosion/Productivity Impact Calculator (EPIC) model to estimate the amount of atmospheric C that could be sequestered by this suggested change in land use. Carbon flow dynamics at each of 100 randomly selected sites were simulated for 50 yr under two assumptions: (i) continuous pasture for 50 yr or (ii) pine plantations harvested every 25 yr. Carbon sequestered by conversion to pine plantations was calculated as the net change in off‐site storage (i.e., in long‐lived products and landfills), plus the change in soil organic C, plus (for the first harvest period) stand establishment. Average C‐sequestration (±SE) was 40 ± 2 and 18 ± 2 Mg C ha−1 for the first and second 25‐yr harvest periods, respectively. In contrast, sequestration would have been 8.3 ± 0.6 Mg C ha−1 as soil organic C if the sites had been left in continuous pasture for 50 yr, or 3 Mg C ha−1 after correcting for release of C during manufacture of N‐fertilizer. Extrapolated to the region, conversion of 3.6 × 106 ha of marginal grass pasture to pine plantations could sequester 5.6 × 106 C yr−1 for the first 25 yr and 1.1 × 106 Mg for the second 25 yr. If all types of marginal agricultural land in the region (4.6 × 106 ha) were converted to forestry, the corresponding sequestration rates would be 7.4 × 10,6 and 1.4 × 106 Mg C yr−1 . In contrast, maintaining the land in continuous pasture would sequester 0.3 × 106 Mg C yr−1.