How do mangroves store CO2?

Mangroves are trees that grow on coasts where the water is warm and salty. They form forests in the upper intertidal zone, mainly in the tropics. The mangrove forest ecosystem includes various species of plants that are adapted to contact with salt water from the ocean and from estuaries: trees, shrubs, palms and ferns. The animals and microbes that live in the mangrove forest are also part of this ecosystem. Both marine and terrestrial life forms come together in this environment, the former below and the latter above. Mangroves provide a nursery for fish and other marine animals.

Mangrove trees extract CO2 from the air and use it to produce oxygen (O2) and carbon (C) through photosynthesis. They incorporate the carbon into their leaves and branches. The coastal forests are inundated regularly by the tides, which bring carbon into the forests in the form of organic material from the remains of plants, animals and other organisms. Depending on environmental conditions, mangroves can store this carbon in sediments for decades, centuries or even millennia. This is because the decomposition of the organic material, which releases CO2, proceeds very slowly in the salty and oxygen-poor sediment.

This means mangrove forests are among the natural habitats that help to mitigate the effects of climate change by binding large amounts of CO2 in their wood and sediment over long periods. To express it in technical jargon, they produce “negative emissions.”

Vorschaubild Video "Negative Emissionen"
Video: Negative emissions (German with subtitles)

Why are mangrove forests threatened?

Threats to mangroves include:

  • Draining the forests to win land for construction
  • Conversion to aquaculture ponds, rice fields, and soy or palm oil plantations
  • Contamination by aquaculture chemicals
  • Pollution from trash and fossil fuel extraction
  • Logging for construction material and fuel

The area occupied by these ecosystems is getting smaller and smaller. Some countries are trying to counteract this trend by planting new mangrove forests, but these efforts are insufficient and often unsuccessful. Preserving this unique and valuable habitat worldwide calls for greater action, stronger protection and better-planned reforestation activities.

Scientific editing: Martin Zimmer, Leibniz Centre for Tropical Marine Research (ZMT)

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