Recovering Tropical Forests Grow Back Nearly Twice as Fast With Nitrogen

Recovering tropical forests are one of the planet’s quiet climate allies. As trees grow, they pull carbon dioxide out of the atmosphere and lock it into wood, roots, and soil, sometimes for centuries. A new large-scale scientific study now shows that this natural climate solution could work much faster than previously thought—if one key nutrient is available in the soil: nitrogen.

The research, published in Nature Communications, reveals that young tropical forests can regrow and accumulate carbon at nearly double the rate when nitrogen is not in short supply. The findings suggest that nutrient limitations, not just land availability or climate, play a major role in how effectively forests can help slow global warming.

Why young tropical forests matter for climate change

Tropical forests store more carbon than any other land ecosystem on Earth. Importantly, about half of all tropical forests today are recovering from past disturbances such as logging, fires, or conversion to agriculture. These regrowing forests are especially powerful carbon sinks because young trees grow quickly and absorb large amounts of carbon dioxide as they build new tissue.

However, land-use disturbances often cause nutrients to leak out of the soil. Among these nutrients, nitrogen is essential for plant growth because it is a core component of proteins, enzymes, and chlorophyll. Without enough nitrogen, trees simply cannot grow as fast, no matter how much sunlight or water they receive.

The new study shows that this nitrogen shortage may be holding back the climate potential of recovering tropical forests more than scientists realized.

The largest nutrient experiment of its kind

The research team, led by scientists from the University of Glasgow and the Cary Institute of Ecosystem Studies, carried out what is now considered the world’s largest and longest-running experiment testing how nutrients affect tropical forest recovery.

The experiment took place in Panama and included 76 large forest plots, each covering about 1,600 square meters (roughly the size of a hockey rink). These plots represented forests at different stages of recovery: newly abandoned agricultural fields, forests regrowing for 10 years, forests regrowing for 30 years, and mature forests that had experienced little human disturbance for centuries.

Each plot received one of four treatments: added nitrogen, added phosphorus, both nitrogen and phosphorus, or no added nutrients at all. Researchers repeatedly measured tree growth, tree death, and carbon accumulation over decades. Some plots have been monitored continuously since 1997, making this dataset unusually rich and reliable.

Nitrogen dramatically speeds up early forest regrowth

The results were striking. In the youngest forests—those growing back on recently abandoned farmland—adding nitrogen increased forest growth by about 95%. In forests that had been recovering for around 10 years, growth increased by about 48% with nitrogen addition.

In practical terms, trees in nitrogen-enriched plots became taller, thicker, and more abundant in a much shorter time. These faster growth rates translated directly into much faster carbon dioxide absorption, especially during the critical first decade of forest recovery.

Interestingly, forests that were 30 years old or older showed no response to added nitrogen. By that stage, nitrogen had already accumulated naturally in the soil, largely thanks to nitrogen-fixing tree species that partner with soil bacteria to convert nitrogen gas from the atmosphere into usable forms.

A surprising result about phosphorus

For decades, many scientists believed that phosphorus, not nitrogen, was the main nutrient limiting tropical forest growth. Tropical soils are often old and heavily weathered, which can reduce phosphorus availability over time.

However, this study found that adding phosphorus had no measurable effect on forest growth at any stage of recovery. This unexpected result challenges long-standing assumptions about how tropical forests function.

One possible explanation is that tropical trees have evolved clever strategies to cope with low phosphorus, such as specialized roots or microbial partnerships that help them access hidden phosphorus sources. The researchers note that phosphorus may still affect other parts of tree biology—such as root systems or fruit production—that were not measured in this study.

The global carbon implications

The climate implications of these findings are significant. The researchers estimate that nitrogen limitation may currently prevent recovering tropical forests from absorbing 470 to 840 million metric tons of carbon dioxide per year.

If young tropical forests worldwide had sufficient nitrogen during their early recovery stages, they could absorb up to 820 million additional metric tons of CO₂ annually for about a decade. That is roughly equivalent to removing over 140 million gasoline-powered cars from the road each year.

While this boost would not increase the total amount of carbon stored by forests in the long term, it would make carbon uptake happen much faster, buying valuable time while societies work to reduce fossil fuel emissions.

Why fertilizer is not the solution

Despite the clear benefits of nitrogen, the researchers strongly discourage the use of synthetic nitrogen fertilizers in forests. Producing fertilizer is energy-intensive, often relying on fossil fuels, and fertilizer runoff can pollute waterways and release nitrous oxide, a greenhouse gas far more potent than carbon dioxide.

Instead, the study emphasizes nature-based solutions. One approach is to ensure that regenerating forests include nitrogen-fixing tree species, such as many legumes. These trees naturally enrich the soil over time, supporting faster forest growth without harmful side effects.

Another recommended strategy is to prioritize forest restoration in areas already receiving high levels of nitrogen pollution from agriculture, industry, or transportation. In these locations, forests can act as natural filters, absorbing excess nitrogen before it damages ecosystems or contributes to greenhouse gas emissions.

Why timing matters so much

A key message from the research is that the first 10 years of forest recovery are critical. This is when nitrogen limitation is strongest and when interventions like species selection can have the greatest climate benefit.

The researchers stress that reforestation is not a replacement for reducing fossil fuel use. However, faster forest recovery can help delay the worst impacts of climate change, providing a narrow but important window for societies to transition to cleaner energy systems.

Extra context: nitrogen and forest ecosystems

Nitrogen plays a central role in nearly all ecosystems, but its availability varies widely. In tropical forests, nitrogen often becomes scarce after land clearing because crops and fires remove nutrients faster than they can be replaced.

Nitrogen-fixing trees are particularly important during forest succession. By enriching soils, they help set the stage for other species to thrive, increasing biodiversity and ecosystem stability over time. This study highlights how closely forest ecology and climate mitigation are linked through nutrient cycles.

What this means going forward

The findings suggest that forest-based climate strategies should focus not just on how much land is reforested, but also on how forests are allowed to regrow. Understanding nutrient limitations can make reforestation efforts more effective, cheaper, and environmentally safer.

As forest disturbances increase worldwide due to deforestation and climate extremes, nitrogen limitation in young tropical forests may become even more important. Recognizing and working with these ecological realities could significantly improve the climate benefits of forest recovery.

Research paper:
https://doi.org/10.1038/s41467-025-66825-2