African dryland trees store less carbon than believed earlier

African dryland trees store less carbon than believed earlier

Subject: ENVIRONMENT

Section: Ecosystem

Context: Study by team including NASA scientists estimates carbon stocks of trees in semi-arid sub-Saharan Africa; calculates 840 million tonnes of carbon locked up.

More on the News:

• There are far more trees spread across semi-arid regions of Africa than previously thought, but the trees also store less carbon than some models have predicted. A new study has taken inventory of nearly 10 billion trees in semi-arid sub-Saharan Africa.
• The team gathered and analysed carbon data down to the individual tree level across the vast semi-arid regions of Africa or elsewhere something that had previously been done only on small, local scales
• The “carbon residence time,” as scientists call it, is very short for grasses and bushes, which grow seasonally, but much longer for trees that grow for years.
• Carbon is constantly cycling between the land, the atmosphere, the ocean, and back. Trees remove carbon dioxide, a greenhouse gas from Earth’s atmosphere during photosynthesis and store it in their roots, trunks, branches, and leaves.
• For this reason, increasing tree cover is often suggested as a way to offset ever-increasing carbon emissions.
• International Crops Research Institute for The Semi-Arid Tropics (ICRISAT) has published a modelling study that revealed how the right combination of fertiliser5, biochar, and irrigation could potentially increase soil carbon by as much as 300 per cent and help mitigate climate change.

Carbon Cycle

Carbon residence time

• Carbon residence time, also known as carbon turnover time or carbon mean transit time, refers to the average length of time that a carbon atom spends in the atmosphere or another carbon pool before it is exchanged with another pool. In other words, it is the time it takes for carbon to move through the carbon cycle.
• Carbon residence time varies depending on the specific carbon pool being considered. For example, the carbon residence time of atmospheric carbon dioxide is relatively short, on the order of a few years, while the carbon residence time of carbon stored in deep ocean sediments can be thousands or even millions of years.

Soil carbon

• Soil organic carbon (SOC) comes from plants, animals, microbes, leaves and wood, mostly found in the first metre or so.
• Soil organic carbon is a measureable component of soil organic matter. Organic matter makes up just 2–10% of most soil’s mass and has an important role in the physical, chemical and biological function of agricultural soils.
• It is critical for crop yield and climate adaptation or mitigation measures, which are heavily reduced by both intensive agriculture and indiscriminate use of chemicals leading to increased carbon emissions.

Benefits

• Increasing SOC through various methods can improve soil health.
• It can contribute to agricultural yield, food security, and water quality, and also reduce the need for chemicals.
• It helps address carbon mitigationand also improves conditions of fresh water, biodiversity, land use and nitrogen use.
• Moreover, carbon sequestration in soils has the potential to offset GHG emissionsfrom fossil fuels by up to 15% annually.
• Utilising this option would thus offer breathing time before other technologies can help to transit to a zero-carbon lifestyle.

How is it achieved?

• There are many conditions and processes that determine changes to SOC content.
• These include temperature, rainfall, vegetation, soil management and land-use change.
• Thus, increasing Soil Organic Carbon involves adopting sustainable agricultural practices to keep these factors in balance.
• The approaches to increase SOC include:
  • reducing soil erosion
  • no-till-farming
  • use of cover crops
  • nutrient management
  • applying manure and sludge
  • water harvesting and conservation
  • agroforestry practices, etc

Carbon sequestration

• It is the process of capturing and storing atmospheric carbon dioxide.
• It is one method of reducing the amount of carbon dioxide in the atmosphere with the goal of reducing global climate change.
• Natural process: Carbon dioxide (CO2) is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land use and agricultural practices, such as converting crop land into land for non-crop fast growing plants.
• Artificial processes: Artificial processes have been devised to produce similar effects, including large-scale, artificial capture and sequestration of industrially produced CO2 using subsurface saline aquifers, reservoirs, ocean water, aging oil fields, or other carbon sinks, bio-energy with carbon capture and storage, biochar, enhanced weathering, direct air capture and water capture when combined with storage.
• Biosequestration: It is the capture and storage of the atmospheric greenhouse gas carbon dioxide by continual or enhanced biological processes. This form of carbon sequestration occurs through increased rates of photosynthesis via land-use practices such as reforestation and sustainable forest management.