Picture: Eraldo Peres/Associated Press. Small farmers staged a protest against the new Brazilian Forest Code outside of the Ministry of Justice in Brasíliain April. The protesters were symbolically chained together to signify being shackled to the interests of large farmers.

[The New York Times] By

SÃO PAULO, Brazil — Brazil’s Congress fiercely debated changing a cornerstone environmental law on Wednesday night, a move conservationists warned could roll back one of the most effective pieces of legislation protecting forests and biodiversity in Brazil and undermine the country’s efforts to slow greenhouse gas emissions.

The debate pitted powerful agribusiness interests and the government’s own plans for infrastructure projects against scientists and environmentalists concerned that the Brazilian Amazon, one of the world’s largest forests, could be reaching a tipping point in its deforestation.

After announcing an agreement late Wednesday, the government’s leader in Congress could not raise a quorum and the vote was pushed to next week.

A group of so-called Ruralistas in Congress, who favor expanding Brazil’s agribusiness, including Representative Aldo Rebelo of the Communist Party, proposed changes to the law that would open up more land for agricultural expansion. Currently the law, known as the Forest Code, requires that 80 percent of a property in the Amazon, and 20 to 35 percent of land in certain other areas, remain forest. The proposed revisions would exempt small farms from those rules, potentially accelerating deforestation, environmentalists said.

“It is a recipe for disaster,” said Thomas E. Lovejoy, of the Heinz Center for Science, Economics and the Environment.

A proposed revision was first submitted to Congress last June that claimed Brazil’s current law, first enacted in 1934, was holding back the country’s economic development.

With some countries scrambling to ensure food security, including China, Brazil stands as the nation with the greatest potential in the world to expand land for cultivation and cattle grazing, agricultural experts say. Despite restrictions in the Forest Code, Brazil has become the world’s largest exporter of beef and second only to the United States in the export of soybeans.

But despite Brazil’s efforts to slow deforestation, scientists say the Amazon is approaching a tipping point where enough tropical biomass has been lost to cause large areas of the forest to shift irreversibly into savanna or other less biodiverse landscapes. Opening up more land to cultivation could reduce rainfall in the Amazon and place vast stretches of the tropical forest at risk of this “dieback,” researchers say. About 18 percent of the Brazilian Amazon has been deforested, according to official figures.

Climactic changes in the rain forest have begun to alarm researchers. The Amazon suffered its worst two droughts on record last year and in 2005. “There are enough signals out there to not rush into this,” Mr. Lovejoy said.

Antonio Nobre, a researcher at Brazil’s National Institute of Space Studies, has complained about the lack of scientific input in the proposed changes to the Forest Code. “If we had more time to debate, we would have an opportunity to construct environmental legislation suitable for the 21st century,” Dr. Nobre said this month.

Some members of the government of President Dilma Rousseff, including her environment minister, have raised questions about the proposed revisions to the law. If it passes the lower house of Congress, it will need to be approved by the Senate. Ms. Rousseff could veto elements of the proposed changes before they become law.

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