Fig Trees Combat Climate Change: Nature’s Resilient Heroes

Welcome, Net Zero News readers! Today, we delve into an intriguing new discovery that intertwines the worlds of botany and climate science. Recent research has unveiled a remarkable capability of certain fig trees, which could significantly enhance our efforts in mitigating carbon dioxide emissions.

Some species of fig trees are now known to possess the extraordinary ability to store calcium carbonate in their trunks. This process effectively transforms parts of the tree into a stone-like structure, enabling it to sequester atmospheric CO₂ over the long term while simultaneously serving as productive fruit trees. This fascinating research was presented at the prestigious Goldschmidt conference in Prague, where an international team of scientists from Kenya, the United States, Austria, and Switzerland shared their findings.

The fig trees in question, native to Kenya, are among the first fruit-bearing trees identified with this unique ability, known scientifically as the oxalate carbonate pathway. All trees engage in photosynthesis, converting CO₂ into organic carbon that constitutes their trunk, branches, roots, and leaves. This process has propelled tree planting into the limelight as a potential strategy for addressing the pressing issue of CO₂ emissions. However, these fig trees go a step further; they utilise CO₂ to create calcium oxalate crystals. When parts of the tree decay, specialised bacteria or fungi convert these crystals into calcium carbonate—the same mineral found in limestone or chalk.

This transformation is significant as it increases the soil pH surrounding the tree and enhances the availability of various nutrients. Notably, the inorganic carbon contained in calcium carbonate typically has a much longer lifespan in the soil compared to organic carbon, making it a more effective method for carbon sequestration.

Dr Mike Rowley, a senior lecturer at the University of Zurich (UZH) and a key presenter at the Goldschmidt conference, remarked, “We’ve known about the oxalate carbonate pathway for some time, but its potential for sequestering carbon hasn’t been fully considered. If we’re planting trees for agroforestry and their ability to store CO₂ as organic carbon while producing food, we could choose trees that provide an additional benefit by sequestering inorganic carbon, too, in the form of calcium carbonate.”

The research team, which includes experts from UZH, Nairobi Technical University of Kenya, Sadhana Forest, Lawrence Berkeley National Laboratory, the University of California, Davis, and the University of Neuchatel, studied three species of fig trees in Samburu County, Kenya. Their investigation focused on how far from the tree the calcium carbonate was being formed and the microbial communities involved in this fascinating process. Using advanced synchrotron analysis at the Stanford Synchrotron Radiation Lightsource, the researchers discovered that calcium carbonate was being formed both on the exterior of tree trunks and deeper within the wood.

Dr Rowley further explained, “As the calcium carbonate is formed, the soil around the tree becomes more alkaline. The calcium carbonate is created both on the surface of the tree and within the wood structures, likely as microorganisms decompose crystals on the surface and also penetrate deeper into the tree. This indicates that inorganic carbon is being sequestered more deeply within the wood than we previously realised.”

Among the three types of fig trees studied, the scientists identified Ficus wakefieldii as the most effective at sequestering CO₂ as calcium carbonate. The team plans to assess the tree’s suitability for agroforestry by quantifying its water requirements and fruit yields, along with conducting a more detailed analysis of how much CO₂ can be sequestered under varying conditions.

Historically, most research on the oxalate-carbonate pathway has been conducted in tropical habitats, focusing primarily on trees that do not produce food. The Iroko tree (Milicia excelsa) was the first identified to possess an active oxalate-carbonate pathway, capable of sequestering one ton of calcium carbonate in the soil over its lifetime.

Calcium oxalate, one of the most abundant biominerals, is produced by many plants, and the microorganisms responsible for converting calcium oxalate to calcium carbonate are also widespread. Dr Rowley noted, “It’s easier to identify calcium carbonate in drier environments. However, even in wetter environments, carbon can still be sequestered. So far, numerous species of trees have been identified that can form calcium carbonate. But we believe there are many more. This means that the oxalate-carbonate pathway could be a significant, underexplored opportunity to help mitigate CO₂ emissions as we plant trees for forestry or fruit.”

The Goldschmidt Conference, known as the foremost geochemistry conference globally, brings together experts from around the world. This year, it is a joint congress of the European Association of Geochemistry and the Geochemical Society (US), with an expected attendance of 4,000 participants. The conference is taking place in Prague, Czech Republic, from July 6-11, 2025.

As we continue to explore innovative solutions to combat climate change, the findings surrounding these remarkable fig trees highlight the importance of looking beyond traditional methods of carbon sequestration. By integrating these trees into agroforestry systems, we can create productive landscapes that not only provide food but also contribute to the essential task of reducing atmospheric CO₂ levels.

In light of this exciting research, it becomes increasingly clear that our understanding of carbon sequestration is evolving. The natural world holds many secrets, and with studies like these, we are beginning to unveil the ways in which various species can aid in our fight against climate change. The oxalate-carbonate pathway may just be one of the many tools in our arsenal for achieving a net-zero future.

As champions of net zero, let us remain vigilant in following such developments and advocating for practices that enhance the resilience of our ecosystems while addressing the urgent climate crisis we face. Together, through innovative science and sustainable practices, we can pave the way for a greener future.