Young tropical forests are one of nature’s most powerful tools to slow climate change, but a new international study shows that their ability to absorb carbon dioxide is being held back by a shortage of nitrogen in the soil. Researchers have found that when this essential nutrient is available, recovering tropical forests can grow almost twice as fast during their early years, allowing them to capture far more carbon from the atmosphere.
The study, published in Nature Communications was coauthored by ecologist Dr. Sarah Batterman of the Cary Institute of Ecosystem Studies and led by scientists from the University of Glasgow. It suggests that nitrogen limitation in young tropical forests could be preventing them from absorbing up to 470 to 840 million metric tons of carbon dioxide each year. If nitrogen were sufficient, these forests could take in as much as 820 million additional metric tons of carbon dioxide annually for about a decade, a window of time scientists say is critical for global climate action.
Trees remove carbon dioxide from the air through photosynthesis and store it in their trunks, roots, and branches for decades or even centuries. While this makes forest recovery a key climate solution, the new research shows that nutrients in the soil play a decisive role in how fast this process happens. According to Dr. Batterman, nitrogen is the main factor limiting how quickly young tropical forests can regrow after disturbances such as logging, farming, or wildfires.
To understand the role of nutrients, scientists conducted the world’s largest and longest experiment of its kind in Panama. They studied 76 forest plots, each roughly the size of a hockey rink, spread across landscapes at different stages of recovery. Some plots were newly abandoned agricultural fields, while others represented forests that had been regenerating for 10 years, 30 years, or several centuries. The plots received different treatments, including added nitrogen, added phosphorus, both nutrients together, or no fertilizer at all. In some areas, the forests have been monitored continuously since 1997.
The results were striking. In recently abandoned farmland, forests with added nitrogen grew 95 percent faster than those without it. In forests that had been regenerating for 10 years, growth was boosted by 48 percent. The difference was clearly visible in the field, with nitrogen-treated plots developing taller, denser trees and storing nearly twice as much carbon in their early years.
In contrast, older forests showed no response to added nitrogen. Researchers believe this is because nitrogen naturally accumulates over time as certain tree species, known as nitrogen-fixers, establish themselves. These trees work with soil bacteria to convert nitrogen from the atmosphere into forms plants can use, gradually enriching the soil and removing the nutrient bottleneck.
One of the study’s most surprising findings involved phosphorus, a nutrient long thought to limit tropical forest growth. Adding phosphorus had no measurable effect on forest regrowth at any stage. This challenges a widely held assumption in forest ecology and suggests that tropical trees may have evolved strategies to cope with low phosphorus levels. Scientists say further research is needed to understand how trees adapt their roots, metabolism, or nutrient use under these conditions.
Despite the dramatic benefits of nitrogen, the researchers strongly caution against using chemical fertilizers in forests. Nitrogen fertilizer is expensive, energy-intensive to produce, and can pollute rivers while releasing nitrous oxide, a potent greenhouse gas. Instead, the team recommends nature-based solutions that work with existing ecosystems.
One approach is to ensure that nitrogen-fixing tree species are included in reforestation and forest restoration projects. Another strategy is to prioritize forest regeneration in areas already receiving high levels of nitrogen pollution from agriculture, industry, or transportation. In these locations, forests can grow faster while also capturing excess nitrogen before it damages waterways or contributes to air pollution.
The climate implications are significant. The amount of additional carbon that could be absorbed by faster-growing tropical forests is roughly equivalent to taking more than 140 million gasoline-powered cars off the road each year. While this extra carbon storage would not last forever, the researchers emphasize that the first 10 years of rapid growth could buy valuable time as societies work to cut fossil fuel emissions and transition to clean energy.
Dr. Batterman notes that reforestation alone cannot solve climate change, but it can help slow its pace. Faster forest recovery can delay the worst impacts of global warming while governments and industries make the deeper structural changes needed to reduce emissions. In a world running out of time, the study highlights how understanding and working with natural nutrient cycles could make one of our oldest climate allies forests even more effective.