Kirschbaum, M.U.F., Saggar, S., Tate, K.R., Giltrap, D.L., Ausseil, A.-G.E., Greenhalgh, S., Whitehead, D. (2012). Comprehensive evaluation of the climate-change implications of shifting land use between forest and grassland. Agriculture, Ecosystems and Environment 150: 123-138.
Abstract. The transition of land between forest and grassland has important implications for greenhouse gas emissions and removals. In this paper, we comprehensively assess, compare and quantify the net climate change impact of shifting land use between temperate forest and grassland. Forests store large amounts of carbon in their biomass, whereas grasslands contain relatively little biomass carbon. These biomass changes tend to dominate the carbon balance under land-use change. Soil carbon stocks usually do not change much after deforestation unless subsequent erosion occurs, but some soil carbon is often lost when grasslands are reforested with exotic plantations. Forest soils usually release little nitrous oxide or methane and can even oxidise small amounts of methane. Grasslands, on the other hand, can release a large amount of nitrous oxide, which may be further increased with fertilisation, and is higher for cattle- than sheep-grazed systems. Grazing animals increase emissions because they decouple the carbon and nitrogen cycle through their excreta. This locally increases nitrogen concentrations to levels that allow it to escape from soils. Ruminant animals can also emit large amounts of methane. Land cover change in addition has direct radiative effects through the amount of solar radiation that is either absorbed by vegetated surfaces or reflected back into space. As forests typically absorb more radiation than grasslands, this slightly negates the greenhouse consequences of changes in carbon storage and methane and nitrous oxide emissions under land-use change.