- A vast tropical savannah comprised of interspersed grasslands and forests, Brazil’s Cerrado is being converted for agricultural purposes at an alarming rate, researchers have found.
- The researchers used satellite data to determine that cropland within a 45 million-hectare study area has doubled over the past decade, increasing from 1.3 million hectares in 2003 to 2.5 million hectares in 2013.
- Crops are replacing the Cerrado’s natural vegetation so quickly, in fact, that the scientists say it could impact the region’s water cycle.
The Cerrado of Brazil is the second-largest ecoregion in the country after the Amazon rainforest — and it is facing just as much pressure from human activities as the Amazon, according to new research.
Destruction of the Amazon has decreased sharply the past decade and a half, but it turns out much of the agricultural expansion that didn’t occur in the world’s largest rainforest has shifted over to the Cerrado — and that could end up impacting the Amazon all the same.
A vast tropical savannah comprised of interspersed grasslands and forests, the Cerrado is being converted for agricultural purposes at an alarming rate, researchers have found. Crops are replacing the Cerrado’s natural vegetation so quickly, in fact, that the scientists, who have published the results of their study in the journal Global Change Biology, say it could impact the region’s water cycle.
“This is the first study to show how intense the deforestation and agricultural expansion in the Cerrado has been in the past decade,” the University of Vermont’s Gillian Galford, a co-author of the study, said in a statement. “It’s clearly a new hotspot for tropical deforestation.”
Galford was part of a team of researchers from the University of Vermont, Brown University and Woods Hole Research Center who studied ten years of satellite data to examine land use changes in the Cerrado’s Matopiba region, where the majority of recent agricultural expansion has occurred.
The team found that cropland within the 45 million-hectare (about 111 million-acre) study area in Matopiba has doubled over the past decade, increasing from 1.3 million hectares in 2003 to 2.5 million hectares in 2013. The researchers determined that almost three-fourths of this agricultural expansion meant the destruction of native Cerrado vegetation.
This could impact the water cycle in the Cerrado and beyond, the researchers said. During the growing season, crops recycle about the same amount of water as native vegetation, but during the dry season agricultural lands generally recycle about 60 percent less water. If agricultural expansion continues, which the Brazilian government is promoting, that could lead to less rainfall and even a delay in the start of the critical rainy season.
“As agriculture expands, it could affect the rainfall regime that supports both natural vegetation and agricultural production – not just in the Cerrado, but also the Amazon,” lead author Stephanie Spera of Brown University said.
Half of the Amazon’s rainfall is recycled water, Spera said, much of it due to prevailing winds that carry Cerrado air masses west, toward the Amazon. Less moisture in those air masses could result in decreased rainfall in the Amazon, which is already projected to experience more severe and widespread droughts as global temperatures rise.
Co-author Jack Mustard, also of Brown University, added that the timing of the rainy season has wide-ranging impacts, for the Cerrado and the Amazon as well as for agricultural operations themselves. “This is nearly all rain-fed agriculture in this region,” he said. “If you start delaying the onset of rainfall, that has implications for what you can grow.”
According to the researchers, however, policies that encourage double cropping could help to mitigate the impacts of agricultural expansion on the Cerrado water cycle.They found that double-cropping land, in which two crops are planted in the same field during a single growing season, causes it to behave more like native vegetation by extending the growing season, which is when cropland evapotranspiration most closely rivals that of native vegetation.
Just two percent of the agricultural land the team studied in Matopiba was double-cropped in 2003, compared to more than 26 percent in 2013. Without that increase, the reduction of water recycling in croplands would probably have been as much as 25 percent worse, the researchers said.
- Spera, S. A., Galford, G. L., Coe, M. T., Macedo, M. N., & Mustard, J. F. (2016). Land‐Use Change Affects Water Recycling in Brazil’s Last Agricultural Frontier. Global Change Biology. doi:10.1111/gcb.13298