NASA - National Aeronautics and Space Administration

Scientists using NASA satellite data have found that clearing for mechanized cropland has recently become a significant force in Brazilian Amazon deforestation. This change in land use may alter the region's climate and the land's ability to absorb carbon dioxide.

Image right: Deforestation in Mato Grosso, Brazil, as seen by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites. Areas still forested in 2004 are green. Deforested areas are labeled in different colors: 2004 deforestation is red, 2003 is blue, and 2002 is yellow. Areas that appear in gray scale are either not part of the Amazon forest ecosystem or were deforested before the time period covered by the analysis. Click image to enlarge Credit: NASA/Douglas Morton, University of Maryland-College Park

A study published online in the September 14, 2006 edition of the Proceedings of the National Academy of Sciences examined cropland expansion in Mato Grosso, the Brazilian state with the highest deforestation rate and soybean production since 2001. Using data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites and information from field observations, researchers found that in 2003 more than 20 percent of the entire annual deforestation in this state was converted to cropland. This finding suggests that the recent cropland expansion in the region is contributing to further deforestation.

The high resolution and daily frequency of MODIS images allows researchers to distinguish vegetation types in greater detail than other satellites. This capability helped the scientists see for the first time that the size of clearings used for crops has averaged twice that of size of clearings used for pasture. Land conversion also occurred rapidly, with about 90 percent of new crops planted within a year of deforestation.

"Deforestation for cropland usually involves clearing several square kilometers of forest and results in greater separation of remnant patches of forest than other land uses," said study lead author Douglas Morton, University of Maryland, College Park, Md. "MODIS data is especially helpful in monitoring these changes because with two daytime observations it provides much better data than other satellites over typically cloudy regions like the Amazon basin to help distinguish different land cover types."

Image left: This image shows burning and deforestation of the Amazon forest to make grazing lands. Click image to enlarge Credit: NASA LBA-ECO Project

In addition to mapping the change in land use type over Mato Grosso between 2001 and 2004, the researchers compared these changes with shifts in agricultural prices in the region. As soybean prices rose in 2003, the conversion from forest to cropland increased while the amount of land converted to pasture declined.

Cropland deforestation also has a more pronounced ecological and climate impact than other land conversions because it involves the complete removal of land biomass, including tree trunks, stumps and woody roots. "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," said co-author Ruth DeFries, University of Maryland. Of all land uses and types, croplands are also one of the least efficient at absorbing carbon from the air.

In a related study, to be published in Earth Interactions, researchers found that the region's climate is impacted not only by the overall extent of clearing, but also by the type of subsequent land use.

Image right: Image of recently planted cropland in Mato Grosso, Brazil. Click image to enlarge Credit: Douglas Morton, University of Maryland-College Park

Using a computer climate model driven by MODIS data, the researchers examined the sensitivities of climate to recent changes in Mato Grosso. Model results indicate that areas converted from tropical forest to cropland, including soybean, result in warmer, drier conditions. But the conversion of forest into pasture - land with grasses - results in a cooling effect.

"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."

These findings suggest that recent land conversions of the Amazon forest may have measurable effects on the regional climate.

Both research studies were supported by the Large Scale Biosphere-Atmosphere Experiment in the Amazon, an international research effort led by the Brazilian Ministry of Science and Technology and sponsored by NASA’s Terrestrial Ecology and Land Use-Land Cover Change Programs.

Related Links:

+ Additional information and images
+ MODIS Satellite page
+ Related Earth Observatory story on Amazon Deforestation
+ Feature story on the Large-Scale Biosphere-Atmosphere (LBA) experiment

Mike Bettwy
Goddard Space Flight Center