Agriculture, Forestry and Other Land Use (AFOLU)

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Credit: pexels.com
Picture Source: pexels.com

IPCC (2006) defines the agriculture, forestry and other land use (AFOLU) sector that all managed land with relating to all direct human-induced effect on greenhouse gas emissions and removals. Land use and management impact diversity of ecosystem processes that influence greenhouse gas flows; for example, photosynthesis, respiration, decomposition, nitrification nitrification/denitrification, enteric fermentation, and combustion. All the biological (activity of microorganisms, plants, and animals) and physical processes (combustion, leaching and run-off) drives transformations of carbon and nitrogen.

The main greenhouse gases in AFOLU are CO2, N2O and CH4. CO2 is absorbed through plant photosynthesis and released via respiration, decomposition and combustion of organic matter; it fluxes between the atmosphere and ecosystem. N2O is a by-product of nitrification and combustion of organic matter and emitted to the atmosphere. CH4 occurs from methanogenesis through anaerobic conditions in soils and manure storage that is from enteric fermentation, and during incomplete combustion in process of burning organic matter. Other indirect greenhouse gas emissions from AFOLU are related to run off of nitrogen compounds, especially, NO3- losses from soils, consequently, some of which can be transformed to N2O via denitrification.

 

The main greenhouse gas emission sources/removals and processes in managed ecosystems
The main greenhouse gas emission sources/removals and processes in managed ecosystems; Cited from IPCC, 2006; Modified by: ERM-Siam Co., Ltd.

The 2006 IPCC Guidelines define the six land-use categories, which are 1) forest land, 2) cropland, 3) grassland, 4) wetland, 5) settlements and 6) other land. These six categories represent different perspectives of land-use and management systems, including stratification of land area by climate, soil and other environmental strata. There are four ecosystem components as the primary ecosystem stocks and processes in the AFOLU Sector, which are 1) biomass, 2) dead organic matter, 3) soils and 4) livestock.

  1. Biomass includes plant biomass, above-ground and below-ground parts; which are major channels for CO2 removal from atmosphere. Most of CO2 are relocated between the atmosphere and terrestrial ecosystems via photosynthesis and respiration. Human activities can induce changes of CO2 by deforestation, afforestation, fertilization, irrigation, harvest, and species choice. For instance, tree harvesting decreases biomass stocks on the land. Some of carbon may relocate from the ecosystem and promptly emit to the atmosphere, meanwhile, some carbon is transferred to other stocks that cause the delayed emissions. In non-forest ecosystems – e.g. Cropland, Grassland –biomass is mostly non-woody perennial and annual vegetation, in which a much smaller part of total ecosystem carbon stocks comparing to the forest lands. This kind of carbon stocks may continue nearly constant. In case of fire use as a management tool in grasslands and forests or wild fire, its cause could lead significantly loses of biomass carbon. Fires affect direct and indirect greenhouse gas emission, from combustion of biomass, for example, CO2, CH4, N2O, NMVOC, NOx and CO.
  2. Dead organic matter (DOM) finally comes from living plant substance. A portion of DOM can indicate time of decomposing, it could be for days to months to years to decades. Losses due to burning dead organic matter include emissions of CO2, CH4, N2O, NMVOC, NOx and CO.
  3. Soils are transferred from dead organic matter which is fragmented and decomposed, called as soil organic matter (SOM). SOM has different components which can be decomposed quickly by microbial organisms; or very slowly retained in the soil for decades to centuries or more. Sooner or later, decomposition of SOM returns carbon to the atmosphere. Soil organic stocks are impacted by land-use and management activities, human activities, climate variability and other environmental factors affected soil carbon dynamics, as well as biomass and DOM. In flooded condition, such as wetland environments and paddy rice production, an important part of the decomposing DOM and SOM is returned CH4 to the atmosphere. This condition can be considered major source of emission in countries in which land dedicated to paddy rice production.
  4. Livestock defines as animal production systems with ruminant animals that can be significant source of greenhouse gas emissions. CH4 is emitted by enteric fermentation in the digestive systems of ruminants. Manure disposal and storage in terms of management decisions influence emissions of CH4 and N2O, which are formed in decomposing manures as a by-product of methanogenesis and nitrification/denitrification, respectively.

 

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Categories: Climate Change,GHG Emission Sources

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