NASA satellites data revealed that clearing to grow crops is now an important element in Brazilian Amazon deforestation since 2001. This may alter the region's climate and the land's ability to absorb carbon dioxide.
Mato Grosso, one of the nine states of Brazilian Amazon, is the Brazilian state with the highest deforestation and soybean production rates. It produced 87% of the increase in Brazilian cropland from 2001 to 2004 and 40% of new deforestation for cropland, about 36,000 square km (more than Belgium's surface).
More than 20 percent of the state's forests were converted to cropland only in 2003. The recent cropland growth in the region triggers further deforestation.
The new improved techniques allow researchers to distinguish vegetation types in greater detail. The scientists could see for the first time that the size of the clearings used for crops has averaged twice the size of clearings used for pasture, making deforestation more environmentally destructive.
Land conversion has also occurred rapidly, with about 90 percent of new crops planted within a year of deforestation. The data contradict previous claims that Brazil's expanding crop production is met by converting land previously cleared for cattle
ranching, although pasture remains the dominant land use. "Deforestation for cropland usually involves clearing several square kilometers of land and results in greater separation of remnant patches of forest than other types of land use," said study lead author Douglas Morton, University of Maryland, College Park, Md.
"MODIS (Moderate Resolution Imaging Spectroradiometer) data is especially helpful in monitoring these changes because its two daytime observations provide much better data than other satellites over typically cloudy regions like the Amazon basin to help distinguish different land cover types."
The researchers observed a strong correlation between the amount of land deforested and the average annual soybean price. The rise of soybean price in 2003 increased the amount of forest land inverted to cropland, while the amount of land converted to pasture fell down. "In 2005, soybean prices fell by more than 25 percent and some areas of Mato Grosso showed a decrease in large deforestation events, although the central agricultural zone continued to clear forests," said Morton.
"But, deforestation rates could return to the high levels seen in 2003 as soybean and other crop prices begin to rebound in international markets."
Brazil is now a world grain producer leader, accounting for more than one-third of the country's gross national product. The changes of prices for other crops, beef and timber will have the leader role in forest loss in the Amazon area.
Changing forest to cropland has a more severe ecological and climate impact, because it involves the complete removal of woody biomass. "The carbon once contained in the living material and soil is released into the air from multiple fires during the clearing process, causing atmospheric carbon dioxide concentrations, a primary greenhouse gas, to increase,"
"We didn't quantify the amount of remaining biomass in the paper, but we suggest that carbon emissions per area will be greater when more biomass is removed", said co-author Ruth DeFries, University of Maryland. Croplands are also one of the least efficient at absorbing carbon from the air amongst all types of land use.
Changes in land use directly influence climate by affecting the amount of absorbed solar heat, its transfer and flow, and plants and soil evaporation, and the cooling process.
The data show that areas converted from forest to cropland result in warmer, drier conditions. But the conversion of forest into pasture results in a cooling effect. Tropical forests generally keep temperatures cooler, because they transpire water through their leaves. Forests can keep a lower temperature than croplands, even during the dry season.
"We found areas deforested and left with bare ground had the most profound impact on climate, raising temperatures up to 3 degrees Fahrenheit," said study co-author Lahouari Bounoua, NASA Goddard Space Flight Center, Greenbelt, Md.
"Forests replaced with croplands had the second most significant climate impact, followed next by pastures."
The tropics receive two-thirds of the world's rainfall. The water circuit dictates storing and releasing heat. With so much rainfall, a large amount of heat is released into the atmosphere affecting regional and global climate.
"This research provides the information needed for programs to reduce deforestation, projections of future deforestation, and efforts to identify priority areas for conservation", said Morton.