Soil carbon sequestration in United States rangelands

Rangelands are uncultivated lands that include grasslands, savannahs, steppes, shrub lands, deserts and tundra. The native vegetation on rangelands is predominantly grasses, forbs and shrubs (Kothmann, 1974). Rangelands cover 31 percent of the land surface area of the United States (Havstad et al., 2009), and up to half of the land surface area worldwide (Lund, 2007). Most land areas that are not developed, not cultivated, not forested and not solid rock or ice can be classified as rangelands. Because of their extent, a small change in soil carbon (C) stocks across rangeland ecosystems would have a large impact on greenhouse gas (GHG) accounts. There are 761 million acres of rangelands in the United States (Havstad et al., 2009), half of which are public lands in the West (Follett, Kimble and Lal, 2001). The primary activity focus on rangelands is grazing. Rangelands and grazing lands are two broadly overlapping categories. United States grazing lands, including managed pasturelands, have the potential to remove an additional 198 million tonnes of carbon dioxide (CO2) from the atmosphere per year for 30 years (Follett, Kimble and Lal, 2001), when saturation is reached. This would offset 3.3 percent of United States CO2 emissions from fossil fuels (EIA, 2009, and help protect rangeland soil quality for the future. The past 20 years have seen a tremendous enhancement in the understanding of soil C, both its role in the global C cycle and the factors that influence its dynamics. Although soil organic carbon (SOC) has long been of interest to scientists, technical advisers and land managers as an indicator of soil health, the link between the C cycle and global climate change has provided increased impetus for quantification and, ultimately, management. Even if atmospheric concentrations of GHGs were quickly stabilized, anthropogenic warming and sea levels would continue to rise for centuries A.J. Fynn, P. Alvarez, J.R. Brown, M.R. George, C. Kustin, E.A. Laca, J.T. Oldfield, T. Schohr, C.L. Neely and C.P. Wong