The potential of Florida grasslands to contribute to C sequestration and climate change mitigation

Abstract

Grassland accounts for 25% of earth's surface and contains approximate-ly 12% of the earth's soil organic matter. It has been estimated that between 29.5 and 110 Tg C can be annually sequestered in grassland systems in the USA. Improved management can further expand grassland mitigation potential by 2 to 8 percent by 2020 while improving the resilience of ecosystems to impacts of climate change. A variety of management practices have been suggested to increase soil C sequestration poten-tial. These include fertilization, grazing management, irrigation, and use of highly productive forage grass and legume species. Because improved management practices are normally benefi-cial to forage and livestock production, they may also provide an incentive for producers to adopt strategies that enhance soil C pools. In addition, C trading-related markets and the growing inter-est in C sequestration as mechanisms for environmental protection are also expected to enhance the economic value of the ecological services provided by grasslands.Despite the increased demand for more intensive land use and conversion of extensively-managed native ecosystems into intensively-managed agriculture or urban development, little is known on how changes in land use and management may affect soil-C sequestration in grass-lands. This is particularly important in the USA where urban development is increasingly competing with natural resources for land. It is evident that reduction of grassland area and manage-ment associated with land use change, will likely cause shifts in community species, C alloca-tion, and thus, may have major impacts on the global C cycling. Therefore, understanding the changes that occur on soil C dynamics as a function of management intensification is essential to predicting C decomposition rates and susceptibility to losses and, consequently, the impacts of grassland management on soil C sequestration and greenhouse gas mitigation potentials. More-over, because of the extensive distribution of grasslands worldwide, science-based information is needed to address ecosystem behavior (i.e. C accumulation rates, partitioning, and allocation, and greenhouse gas emissions) in response grassland management practices. We also expect that by increasing soil C sequestration will have significant impacts on the overall soil quality and can potentially contribute to the sustainability of grassland ecosystems in the USA.The long-term goal is to provide a scientific basis for improving resilience of grassland ecosystems and thus, adaptation to climate change. The overall objective of this project, which is a step toward attainment of our long-term goal, is to determine the long-term (> 15 yr) impacts of land use conversion from native rangelands into intensively-managed improved pastures on the amounts and characteristics of soil C stocks and greenhouse gas emissions and through different forms of grassland management. The central hypothesis is that management practices intended to increase biomass and livestock production and land use intensification, such as converting range-lands into improved pasture systems and introduction of grazing livestock, control organic matter production, distribution and quality and, therefore, have major effects on C sequestration and greenhouse gas emissions in grassland systems. The rationale for studying the characteristics of soil C in the context of intensive grassland management systems is that agriculture accounts for ~ 14% of global greenhouse gas emissions or about 6.7 Gt of CO2 equivalent per year. Greenhouse gas emissions from land use change represent ~ 17% of total. Thus, sustaining productivi-ty on existing land use and potential restoration of degraded grasslands can be an attractive economic mitigation option to reduce greenhouse gas emissions. (AU)