At a time when the impacts of climate change are accelerating and the need for natural and sustainable solutions is growing, a new study has revealed that certain fig tree species store calcium carbonate in their trunks, partially transforming them into rocks.
A team of Kenyan, American, Austrian, and Swiss scientists found that these trees are capable of absorbing carbon dioxide (CO₂) from the atmosphere and storing it in the form of calcium carbonate rocks within the surrounding soil.
These fig trees—native to Kenya—are among the first fruit trees proven to possess this capacity, known as the “oxalate–carbonate pathway.”
Fig Trees as Natural Carbon Reservoirs
All trees use photosynthesis to convert carbon dioxide into organic carbon, which forms their trunks, branches, roots, and leaves. For this reason, tree planting is widely seen as a potential strategy to mitigate CO₂ emissions.
Some trees also use carbon dioxide to form calcium oxalate crystals. When parts of the tree decay, specialized bacteria or fungi convert these crystals into calcium carbonate—the same mineral found in limestone or chalk. This process not only raises the pH of the soil around the tree but also enriches it with higher levels of nutrients.
Inorganic carbon stored as calcium carbonate generally remains in the soil much longer than organic carbon, making it a more effective method of carbon sequestration.
Scientific Evidence of the Importance of Fig Trees
Dr. Mike Rowley, Senior Lecturer at the University of Zurich (UZH), presented the research at the Goldschmidt Conference, the world’s leading geochemistry meeting, co-organized by the European Association of Geochemistry and the Geochemical Society in the Czech Republic.
Rowley explained:
“We have known about the oxalate–carbonate pathway for some time, but its potential for carbon sequestration has not been fully studied. If we are planting trees for agroforestry purposes—for their ability to store CO₂ as organic carbon while also producing food—we could select species that additionally provide the benefit of storing inorganic carbon as calcium carbonate.”
A research team from the University of Zurich, Technical University of Nairobi in Kenya, Sadhana Forest, Lawrence Berkeley National Laboratory, the University of California, and the University of Neuchâtel studied three species of fig trees cultivated in Samburu County, Kenya.
Among the three species examined, scientists found that Ficus wakefieldii was the most effective at sequestering CO₂ in the form of calcium carbonate.
The researchers now plan to assess the suitability of this species for agroforestry by determining its water requirements, fruit productivity, and conducting a more detailed analysis of how much CO₂ can be sequestered under different conditions.
