Reforestation can Sequester Globally Significant Amounts of Soil Carbon
Within a century, carbon accumulation in topsoils of U.S. land areas undergoing reforestation could exceed 2 Pg carbon.
Reforestation of marginal croplands and active replanting on understocked forest lands are two promising strategies for increasing soil carbon sequestration. The rate of carbon accumulation in surface soils of lands already undergoing reforestation in the continental United States was quantified by combining 15,000 soil profile observations with remote sensing and geospatial information.
This study provides the first empirical estimate for the role of reforesting topsoils in U.S. forest carbon sequestration. The results suggest that the carbon sink associated with the surface soils of lands currently undergoing reforestation could persist for decades, providing more than 10% of the total forest sector carbon sink through the 21st century.
Soils can act as either a source or a sink of atmospheric carbon, depending on land use and management. Data associated with 15,000 soil profile observations were integrated with remote sensing and geospatial information to quantify changes in surface soil carbon stocks associated with lands undergoing reforestation across the continental United States. Currently, these reforesting lands occupy >500,000 km2 and accumulate 13 to 21 terragrams of carbon (Tg C) per year in surface soils. Annually, these soil carbon gains represent 10% of the entire forest sector carbon sink, effectively offsetting 1% of all U.S. greenhouse gas emissions. Although the surface soils of existing reforesting lands are projected to sequester a cumulative 1.3 to 2.1 Pg C within a century, additional replanting of understocked forest lands and further efforts to convert marginal cropland to forest could significantly increase forest sector carbon sequestration. This study provides new observational benchmarks to constrain model projections of the role of reforestation in the U.S. carbon budget and the magnitude and longevity of the U.S. forest carbon sink.
Julie D. Jastrow
Argonne National Laboratory
Argonne National Laboratory
This study was supported by the U.S. Department of Agriculture Forest Service, Northern Research Station Agreements 13-CR112306-077 and 16-CR-112306-071, National Science Foundation Award EF-1340681, and Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, under contract DE-AC02-06CH11357.
Nave, L.E., Domke, G.M., Hofmeister, K.L., Mishra, U., Perry, C.H., Walters, B.F, & Swanston, C.W. “Reforestation can sequester two petagrams of carbon in US topsoils in a century”. Proceedings of the National Academy of Sciences USA 115(11), 2776– 2781 (2018). [DOI:10.1073/pnas.1719685115]