Satellite imagery shows drastic South American deforestation

April 2, 2021

Where are we clearing land, and what are we using it for? (AP Photo/Andre Penner)

The amount of South American land impacted by humans skyrocketed 60% from 1985 to 2018, and an area the size of Spain has been cleared by humans but is not being used for any discernible economic purpose, according to new research using satellite images and machine learning technology. 

By converting natural land for purposes such as farming and ranching, as well as through logging and fires, humans have impacted formerly natural land at a rate of 21.6 soccer fields per minute since 1985, international researchers led by a group from the University of Maryland said in a new Science Advances paper

The degradation of formerly natural South American land has a variety of consequences, including exacerbating climate change by removing large swaths of carbon-absorbing rainforest and killing off endangered species of plants and animals. Many of the natural areas being devastated by humans were also formerly home to Indigenous groups, some of whom have been driven off ancestral land and killed

"We're running out of time. You cannot keep converting things at this rate," said lead author Viviana Zalles, a postdoctoral researcher with the University of Maryland's Global Land Analysis & Discovery group. "We depend on nature for clean air, for clean water, for protection from climatic events, floods, droughts."

The ongoing destruction of the Amazon rainforest for purposes such as farming, ranching, and oil and gas extraction has been widely documented in recent years. But the finding that a Spain-sized amount of land — 55 million hectares, or more than 210,000 square miles — has been cleared by humans and then left alone came as a surprise, Zalles said. The researchers labeled it "transitional land," classified as cleared land that has been changed by humans and then left alone for at least three years. 

"This category of land we didn't really know about before," she said. "For South America, that's something that's not really talked about in the literature." 

The causes of land being cleared and then abandoned may include failed attempts at farming and ranching, migration to urban centers, and the fact that in some regions, individuals can become legally entitled to a tract of land if they show they've made an attempt to clear it, Zalles speculated. She said she hopes that other researchers will examine the issue in greater depth. 

Zalles and her team, which also included researchers from the State University of New York; the Federal University of Goiás, in Brazil; and Texas Tech University, utilized decades of satellite images made public by the U.S. government. 

"The satellite is orbiting the Earth and consistently taking pictures, and we use machine learning algorithms to distinguish between new kinds of land-use patterns," Zalles said. "Based on the surface reflections of the Earth, we can apply these algorithms and separate out, classify and make maps." 

After running the images through the machine learning algorithm, the researchers then selected and tested a stratified random sample in order to produce a confidence interval for each of their results. 

In addition to examining South America as a whole, the researchers also studied land-use changes by country. Brazil was the most affected country by far, Zalles said, with a quarter of all natural land impacted by humans during the 34-year study period. That human expansion has been driven by demand for pasture land, she said. 

In Argentina, by contrast, deforestation has been much less of an issue than in Brazil, according to Zalles. However, much of the country's older pasture land has been converted to farmland for commodity crops such as soy and corn, which are generally tougher on the land than cattle, because they require large amounts of water, fertilizer and pesticides, Zalles said. 

As agricultural production in North America has declined as a share of the global total, South America has rapidly become the center of the world's soy production, producing just a quarter of global soy in 1985 but over half in 2018, the researchers found. South America is also the world's largest producer of beef and is second after East Asia in corn production. 

Zalles said she is working on an upcoming paper about soy production's impact on deforestation. She also plans to apply similar satellite image and machine learning-based techniques to examine land-use changes around the world. 

As a geographical sciences specialist, Zalles expressed frustration that she sometimes feels pressure from journal reviewers to more explicitly connect land-use issues to climate science by, for example, including an estimation of the land-use changes' effect on carbon emissions. 

"The part that we do — the remote sensing, mapping, quantification of the ways the land is changing over time — is a science in and of itself," she said. "If I tell you 26 soccer fields per minute every single minute for 34 years [have been impacted by humans], you don't think that has impacts for emissions and biodiversity? Of course it does."

Deforestation in countries like Brazil and Argentina is driven in large part by demand from regions like the U.S. and Europe. A study published in Nature Ecology & Evolution earlier this week found that countries, like the U.S., that tout protections of forests within their borders are driving deforestation abroad. 

The paper, "Rapid expansion of human impact on natural land in South America since 1985," published April 2 in Science Advances, was authored by Viviana Zalles, Matthew C. Hansen, Peter V. Potapov,, Diana Parker, Amy H. Pickens, Andres Hernandez-Serna and Indrani Kommareddy, University of Maryland; Stephen V. Stehman, State University of New York, Syracuse; Leandro Leal Parente and Laerte G. Ferreira, Federal University of Goiás; and Xiaopeng Song, Texas Tech University. 

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