Recovering tropical forests grow back nearly twice as fast with nitrogen
Published: 13 January 2026
New research suggests that that if recovering tropical forests had enough nitrogen in their soils, they might absorb up to an additional 820 million metric tons of carbon dioxide each year for a decade.
Young tropical forests play a crucial role in slowing climate change. Growing trees absorb carbon dioxide from the air, using photosynthesis to build it into their roots, trunks, and branches, where they can store carbon for decades or even centuries.
But, according to a new study, this CO2-absorption may be slowed down by the lack of a crucial element that trees need to grow: nitrogen.
In a new paper published in the journal Nature Communications, researchers from the University of Glasgow in the UK and the Cary Institute in the USA suggest that that if recovering tropical forests had enough nitrogen in their soils, they might absorb up to an additional 820 million metric tons of carbon dioxide each year for a decade.
“Nitrogen is limiting how quickly young forests can regrow,” said Dr Sarah Batterman of the Cary Institute, senior author on the paper. “When we added nitrogen to the soil, they grew back almost twice as fast in the first 10 years. Faster growth rates mean faster absorption of carbon dioxide, which can help to give us a few more years to reduce our carbon emissions.”
To increase soil nitrogen and speed up carbon absorption, the scientists recommend planting nitrogen-fixing trees in regenerating forests, and strategically locating these forests on lands with high nitrogen pollution. They advised against widescale application of nitrogen fertilizer, which can have negative environmental impacts.
About 50% of tropical forests are recovering from disruptions such as logging, wildfire, and agriculture — all processes that can cause nitrogen to leak out of the soil. Phosphorus is also thought to be a limiting nutrient in tropical forests.
Scientists, led by Dr Wenguang Tang at the University of Glasgow’s School of Geographical & Earth Sciences, wanted to test how adding nitrogen and phosphorus fertilizers would affect the growth rates, and therefore carbon absorption rate, of tree trunks and branches in recovering tropical forests.
The experiment encompassed 76 hockey-rink-sized plots in Panama, each covering 1600 square meters. The plots ranged in maturity at the start of the experiment, including newly regenerating forests, middle-aged forests that had been regenerating for 10 and 30 years, and mature forests with limited human disturbance for hundreds of years. The plots received additional nitrogen, phosphorus, both, or none. Some of the sites have been monitored since 1997.
“Our work represents the world’s largest and longest nitrogen and phosphorus addition experiment of its kind,” said Dr Tang. “Each of our 76 plots has been censused at least five times, and in each census, data were collected from more than 20,000 trees. Maintaining high-quality, consistent census data over such a long period and across so many individuals was extremely challenging.”
The team found that adding nitrogen caused the forest to regrow a whopping 95% faster in recently abandoned agricultural fields, and 48% faster in the forests that had been regenerating for 10 years.
“It was pretty amazing to see,” said Dr Batterman. “The plots with added nitrogen looked so much bigger than the ones where we didn’t add nitrogen — the trees were just huge. We were surprised how quickly the forest grew back and how strong the effect of nitrogen was.”
For the forests 30 years and older, adding nitrogen had no effect, likely because nitrogen had built up in the soil over time, thanks to nitrogen-fixing trees. These trees cooperate with bacteria to pull nitrogen gas out of the atmosphere, converting it into a form of nitrogen that plants can use.
Contrary to scientific expectations, adding phosphorus to the soil made no difference to forest growth rates at any age — a striking result, said lead author Tang. “This result challenges the long-standing theory that tropical forest carbon sinks are fundamentally constrained by phosphorus availability.”
It is possible phosphorus addition did result in changes to the trees’ roots or fruits, which were not measured in this study. Another explanation is that trees in these forests have evolved creative ways to overcome phosphorus limitations. The scientists hope to investigate this thread further, to better understand what strategies the trees are using to maintain high productivity despite low phosphorus in the soil.
“Future work should also examine how consistent these patterns are in other tropical forests, including in Africa and Asia,” said Dr Tang. “However, we expect nitrogen limitation in young tropical forests may be quite common. It’s likely becoming increasingly important, too, as forest disturbances increase and carbon dioxide levels rise in the atmosphere.”
If nitrogen limitation is indeed widespread, the team estimates it may prevent recovering tropical forests from absorbing an additional 470 to 840 million metric tons of carbon dioxide per year. That’s roughly equivalent to taking 142 million gasoline-powered cars off the road each year.
To achieve those gains, the team does not advocate for adding fertilizer to overcome nutrient limitations. Nitrogen fertilizer is expensive and energy intensive to produce; it can also pollute waterways and lead to emissions of nitrous oxide, a powerful greenhouse gas. Instead, the team recommends being more strategic about where to focus on forest regeneration, and which tree species should be planted at these sites.
“Ideally, forest stewards could make sure that some of the trees in a regrowing forest are nitrogen-fixers,” said Dr Batterman.
Another strategy recommended by the team is to prioritize reforestation in areas where there is high nitrogen pollution from agriculture, factories, and transportation. This way, the trees can clean up the nitrogen pollution before it clogs waterways or turns into greenhouse gases, and the forests will grow back faster.
“These practices could increase how quickly these recovering forests take in carbon dioxide,” said Dr Batterman. “In the long-term, the forests are not going to sequester extra carbon, but in that first 10 years they can do the job faster, and 10 years is what we really need right now. We need to make big changes to reduce our fossil fuel emissions, such as shifting to clean energy and swapping out our gas guzzlers for electric vehicles, and unfortunately that switch is taking longer than we need it to. Reforestation is one tool that can buy us more time to decarbonize and delay the worst effects of climate change.”
The team’s paper, titled ‘Tropical forest carbon sequestration accelerated by nitrogen’, is published in Nature Communications.
First published: 13 January 2026