January 23, 2021


It's Your Education

Brazil scientists map forest regrowth keeping Amazon from collapse: Study

  • Scientists have mapped Brazil’s secondary forests and are now able to pinpoint the extent, age and location of regrowing vegetation anywhere in the country, opening up opportunities for incentive programs, monitoring and forest fire prevention.
  • According to their findings, 12% of total carbon emissions from Amazon deforestation have been offset by Brazil’s secondary forests, making natural regrowth an underestimated tool for mitigating global carbon emissions and regional ecosystem collapse.
  • About a third of Brazil’s lost forests have recovered naturally, but without halting deforestation of primary forest, regrowth efforts will be redundant in offsetting emissions, the study authors say.
  • Brazil’s secondary forest map can be used as proof that areas are being protected, making it easier to monitor and create incentives for farmers and landowners with secondary forests on their land.

When Celso Silva Junior, a Ph.D. candidate at the Brazilian Institute for Space Research (INPE), stepped back from his recently completed map of Brazil’s secondary forests, he was surprised by the sheer quantity that had grown back since the 1980s.

About a third of Brazil’s lost forests have recovered naturally, an area approximately the size of the United Kingdom — 262,791 square kilometers (101,464 square miles), according to the map Junior published in a recent study in the journal Scientific Data in collaboration with 11 other researchers.

But until the article’s publication this past August, scientists didn’t know the exact extent of forest regrowth in Brazil, how old these forests were, or where they were located. Now, the authors of the study told Mongabay, the maps can be used to support recovery, track deforestation patterns, and even prevent wildfires.

Recovery forest in the Brazilian Amazon. Image by Celso Silva Junior.

“If every seven years, secondary forest is cut down, then you know that in a six-year-old secondary forest in that region, fire or deforestation is imminent,” said co-author Liana Anderson, a researcher at Brazil’s National Center for Monitoring and Early Warning of Natural Disasters.

During a dry year, authorities can use this information to prevent large forest fires and clear-cutting before it happens. “It’s better to plan ahead instead of dealing with the damage, which is what has been happening in the last two years,” Anderson said, in reference to the reactive approach by the government of President Jair Bolsonaro to deforestation and forest fires.

Much of the Amazon’s secondary forests are born from extensive pasture land that has lost its commercial productivity. Soil fertilization isn’t widely practiced, and land management is largely inadequate. So as the rainforest soil loses its nutrients, many farmers move on to new areas, abandoning large areas of former pasture that then regrow naturally.

While traditional communities rotate small-scale farmland to retain fertility, which may be detected as secondary forest area by satellites after a few years, these century-old practices have coexisted with the rainforest ecosystem, unlike the vast swathes of cattle pastures responsible for much of the deforestation in the Amazon.

Vegetation may also regrow when land grabbers speculate on cleared lots, leaving them unattended, and when aspiring farmers are forced to abandon land after bad planning, illegal settlements and cash shortages means they aren’t able to successfully set up pastures or cropland after clear-cutting. A 2019 report by the Climate Policy Initiative identified that approximately 40% of the deforested land in the Brazilian Amazon’s protected areas were undergoing a process of regeneration by 2014, amounting to approximately 2 million hectares (5 million acres).

Undisturbed, even if just for a year, deserted areas often start a slow but continuous process of growing back. Only after at least 15 years does this new vegetation begin to resemble a forest. And it takes 40 years on average for secondary forests in the Amazon to recover 85% of their original biodiversity, a 2018 study concluded.

Researchers warn that there is no long-term guarantee for forest restoration: secondary forests are targeted for deforestation as they are easier to clear, and are often in areas with fewer legal protections.

By overlapping secondary forest maps with the whereabouts of traditional communities as well as both small and large privately owned pastures and farmland, researchers and policymakers in Brazil can get a clearer picture of the different agricultural dynamics — and ultimately direct policy more effectively, the study authors told Mongabay.

“Now that we know where these regrowth forests are, we need to create mechanisms to protect them,” said lead author Junior. “In the Amazon, secondary forests are more deforested than primary forests. They are much more vulnerable.”

In the study published in Nature, the group of scientists developed a histogram of secondary forest age for each Brazilian biome. The dashed black lines represent the age threshold where more than 50% of secondary forests are accumulated. Image ceded by the authors of the study.

Secondary forests preventing ecosystem collapse

Scientists have long suspected that natural regeneration from abandoned cattle ranches and croplands in the Amazon — about 23% of the destroyed forest territory — acts as a stealthy undercurrent against the global climate crisis.

Leading experts Carlos Nobre and Thomas Lovejoy say the Amazon’s secondary forests are preventing an ecosystem collapse. “These areas, which now lay fallow, are probably the main reason why the Amazon has not already become an expanding savannah,” the pair wrote in a 2019 letter published in Science Advances.

Allowing abandoned land to regenerate is the cheapest way to large-scale forest recovery, especially in the Amazon, Anderson told Mongabay. Without the costs and manual labor associated with tree planting, simple management measures can ensure the restoration of huge areas of damaged forest, with benefits to local biodiversity and carbon storage.

As secondary forests grow, the study shows, they absorb carbon at higher rates than mature, old-growth forests, which are often carbon neutral. And according to a recent global report, secondary forests have been overlooked as a key tool for dealing with the global climate emergency.

In Brazil, these areas have already compensated for 12% of emissions from Amazon deforestation, according to the authors’ calculations. Restoring 12 million hectares (29.6 million acres) of forest area by 2030 under the Paris Climate Agreement is one of Brazil’s key commitments.

But researchers warn that if forest destruction doesn’t stop, regrowth efforts may become redundant. Scientists agree that a conservation strategy combining the protection of primary forests, where large amounts of carbon are stored, and the regeneration of secondary forests is essential for a successful outcome.

Under Bolsonaro, who took office at the start of 2019 and is leading an aggressive pushback against environmental protections, Amazon deforestation has increased by 47%. The deforestation rate hit a 12-year high of 11,088 square kilometers (4,281 square miles) between August 2019 and July 2020, according to the latest data published by INPE. Major fires also consumed the Amazon and Pantanal biomes this year.

Maps to save Brazil’s forests

The federal government hasn’t adopted policies to protect secondary forests. But the state of Pará in the eastern Amazon has already made progress. Joice Ferreira, a leading researcher at the Brazilian Agricultural Research Corporation, helped create state legislation in 2015 to protect older secondary forests, based on her regional mapping research.

“We suggested that after 20 years, cutting down secondary forests should be banned. We needed this law to protect these areas,” Ferreira told Mongabay, “For farmers, one-year-old regrowth is what they call a dirty pasture. But it’s the beginning of natural reforestation.”

In the rest of the Amazon, however, there aren’t any measures in place to protect or encourage this growth. “In other states, these laws don’t exist yet. But a study like this can help other states manage these areas,” said Ferreira, who did not contribute to the recent study but published another study on reforestation in September 2020 with the similar finding that regrowth in the Amazon alone has offset 10% of its deforestation-driven carbon emissions.

Annual data on land cover and use, and also on land use changes in Brazil over a 34-year period. Data and Image by Mapbiomas.

The Brazil-wide maps open the gates to a potential compensation system that gives landowners an incentive to protect growing forests on privately owned land, says Robin Chazdon, a forest ecologist and author of the book Second Growth. “If we want to encourage farmers to protect these forests, which have huge benefits for biodiversity, ecosystem services, and carbon storage, there needs to be compensation,” she said.

For Junior, this would be one of the best future uses for the maps he helped develop. “[The maps] can be used to monitor future reforestation, create a reforestation plan and pay the people protecting that land,” he said. “And you have proof that it’s standing.”



Silva Junior, C. H. L., Heinrich, V. H. A., Freire, A. T. G., Broggio, I. S., Rosan, T. M., Doblas, J., … Aragão, L. E. O. C. (2020). Benchmark maps of 33 years of secondary forest age for Brazil. Scientific Data, 7(1), 269. doi:10.1038/s41597-020-00600-4

Smith, C. C., Espírito‐Santo, F. D. B., Healey, J. R., Young, P. J., Lennox, G. D., Ferreira, J., & Barlow, J. (2020). Secondary forests offset less than 10% of deforestation‐mediated carbon emissions in the Brazilian Amazon. Global Change Biology26(12), 7006-7020. doi:10.1111/gcb.15352

Lovejoy, T. E., & Nobre, C. (2019). Amazon tipping point: Last chance for action. Science Advances5(12), eaba2949. doi:10.1126/sciadv.aba2949


Banner Image: Large-scale farming is one of the biggest threats for the Amazon rainforest. Photo by Florian Kopp.

Article published by Thiago Medaglia
Agriculture, Biodiversity, Climate Change, Conservation, Deforestation, Environment, Environmental Politics, Forests, Governance, Logging, Plantations, Rainforest Conservation, Rainforest Deforestation, Rainforest Destruction, Threats To Rainforests, Tropical Forests