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.
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