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Rewilding key to averting mass extinctions and reducing carbon emissions

Tiger Leg Monkey Tree Frog (Phyllomedusa hypochondrialis) in Brazil. Photo by Rhett A. Butler/Mongabay.

  • A recent study that analyzed data from biomes all over the world, covering an area of almost 3 billion hectares (7 billion acres) that were turned from natural habitats into farmlands, concluded that rewilding is key to recovery.
  • Restoring 30% of this area and preserving remaining natural habitats could remove almost half the carbon dioxide surplus humans have emitted since the start of the Industrial Revolution.
  • Restoring this area would also save 71% of animal species from extinction compared with current extinction rates, according to researchers.
  • High-priority areas are concentrated in the tropics. Wetlands restoration has the highest positive impact for biodiversity conservation and forests the highest importance for climate change mitigation.

An international team led by Brazilian researchers recently published a study in the journal Nature showing that restoring habitats that are currently degraded by agricultural activity is key to mitigating climate change impacts and avoiding animal species extinction.

The study analyzed data from 2.87 billion hectares (7.09 billion acres) of natural areas worldwide that were transformed into farmland over the years, assessing forests, grasslands, shrublands, wetlands and arid ecosystems all over the globe.

Researchers used three criteria to evaluate optimal outcomes — biodiversity conservation, mitigation of climate change, and costs — with the best restoration solutions combining the highest biodiversity conservation and climate change mitigation with the lowest costs possible. They modeled 1,200 scenarios combining these elements using different restoration approaches.

They note that different objectives point out distinct restoration areas and strategies: recovery of forest areas is the priority when the goal is to mitigate climate change effects, while the restoration of wetlands is of the highest importance when the objective is to conserve biodiversity. Arid ecosystems and grasslands are the most cost-effective areas for restoration.

Though all continents harbor areas that best combine the three criteria, most of the priority areas for restoration were determined to be in the world’s tropics. Preserving natural habitats and restoring 30% of the total converted lands focusing in these regions would save 71% of animal species from extinction and absorb 465 gigatonnes of carbon dioxide from the atmosphere — roughly half of all carbon emitted since the start of the Industrial Revolution.

Gislene Ganade, coordinator of the Restoration Ecology Laboratory at the Federal University of Rio Grande do Norte, says this is the first study to piece together advanced modeling methodology and focus on biodiversity conservation, climate change mitigation and overall restoration costs globally. “There are several restoration studies with different recovery techniques to all ecosystems, but I don’t know one that has used these three criteria at the same time globally before,” Ganade, who did not participate in the study, told Mongabay in an interview.

This research sounds the alarm for policymakers and citizens at a time when the world is entering the Decade on Ecosystem Restoration starting next year as defined by the United Nations, Ganade says. “It shows that Brazil is a leader in restoration studies and also helps to look at a global problem with deep local implications. If there’s a time to talk about these issues, it is definitely now,” she adds.

The study at the global scale was inspired by the same methodology that lead author Bernardo Strassburg, a researcher at the Pontifical Catholic University of Rio de Janeiro, developed to map priority areas for restoration in the Atlantic Forest, one of the most degraded biomes in Brazil.

Restoration, the authors note, does not need to come at the expense of agricultural production, since 55% of converted lands could be restored while maintaining current yields.

he Atlantic Forest is a biome in the top 5 % highest priority for restoration. The image shows a portion of the biome at Serra do Caparaó, at the limits between Espírito Santo and Minas Gerais states. Credits: Heris Luiz Cordeiro Rocha/ Wikimedia Commons, CC BY 3.0

Differing views

The approach the researchers used, however, has its critics. Giselda Durigan, a researcher at the São Paulo State Forest Institute, who did not participate in the study, says she considers the criteria to be fruit of a “pragmatic economist view,” since it focuses on restoration in areas “where it is easier and cheaper to do.”

Durigan told Mongabay that “it is important to heal Earth’s wounds where they are deepest, where natural areas are degraded the most and where there is more pollution and water scarcity — and these areas do not always match with what the study found.” The areas Durigan highlights are mostly in the global north. Restoring areas at fountainheads and riverbeds are of special importance for the maintenance of water in volume and quality, but this isn’t mentioned in the study, she adds.

Strassburg says he agrees with Durigan’s assertion. “Restoring fountainheads is extremely necessary and when we work on modeling at the local scale, we come across this sort of priority,” he told Mongabay.

The study, however, was not able to merge such specific modeling because of its scale. There are a number of factors to take into account when working with such fine-grained models, “from the type of soil in riverine areas to river inclination and its curve type,” Strassburg says. “It is possible to work with such data on a local scale. At the global scale, this is not yet computationally possible.” He adds that, despite mapping restoration areas in a grid of 9-hectare (22-acre) cells, they used much larger cells of 2,500 hectares (6,200 acres) to optimize the final modeling. “Within these cells it makes all sense to prioritize fountainhead areas for restoration. Both approaches work well together,” he says.

Semi-arid farmland in Kenya. The study led by Bernardo Strassburg oversees the restoration of farmland to their natural ecosystems to halt biodiversity loss and mitigate climate change effects. Credits: Andrew Wu, World Resources Institute, CC BY-NC-SA 2.0.

The role of forests and a glimpse of what is possible

More than half of the converted lands the study mapped were originally forest regions (54% of the total). Twenty-five percent of the area was grasslands, 14% shrublands, 4% arid lands and 2% wetlands.

Recovering forest areas is crucial to mitigating the effects of climate change, but many forest areas in priority regions such as Brazil are seeing their areas shrink instead of expanding. The Amazon Rainforest has had more fires this year than in 2019 (more than 89,600 to date against 89,176), when the smoke was so massive that it blacked out the skies in São Paulo, more than 2,700 kilometers (1,700 miles) away.

In the Atlantic Forest, a region that harbors 70% of Brazil’s population, the situation is even more critical. Originally, the biome covered parts of the Brazilian northeast and all states in the southeast and south, including Rio de Janeiro and São Paulo, Brazil’s most populated cities. But today, little more than 12% of its total vegetal cover is left. The study shows the biome is in the top 5% of priority areas for global restoration, Strassburg says.

Deforestation between 2018 and 2019 was almost 30% higher than in the period from 2017 and 2018, according to the SOS Mata Atlântica Foundation and INPE, Brazil’s national space research institute. Restoring and maintaining the forests in such populous regions are essential for the water maintenance Durigan calls attention to.

But there are actions trying to counter the trend.

Strassburg says initiatives such as the Pact for the Atlantic Forest Restoration — aiming to restore 15 million hectares (37 million acres) of native forest — have been very important in the attempt to mitigate part of the habitat loss in the area. “There have been several restoration initiatives in priority places that we mapped in this study and in previous ones. There are actions of several kinds, from natural restoration to assisted natural restoration, led by local groups, cooperatives and large companies,” he says. One example is the Restoration Task Force, led by the Environment Secretariat in the city of Rio de Janeiro, an ongoing reforestation program in the Atlantic Forest region since 1994.

Another of these initiatives, led by photographer Sebastião Salgado’s Instituto Terra, won the E-Award for education from the United Nations at the Rio+20 Conference in 2012. On the occasion, they had planted more than 1.7 million trees in the Atlantic Forest.

Banner image: Tiger Leg Monkey Tree Frog (Phyllomedusa hypochondrialis) in Brazil. Photo by Rhett A. Butler/Mongabay.


Strassburg, B. B. N., Iribarrem, A., Beyer, H. L., Cordeiro, C. L., Crouzeilles, R., Jakovac, C. C., … Visconti, P. (2020). Global priority areas for ecosystem restoration. Nature586(7831), 724-729. doi:10.1038/s41586-020-2784-9

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