In 2006, Greenpeace launched a campaign exposing deforestation caused by soy production in the Brazilian Amazon. In the previous year, soy farming expanded into more than 1,600 square kilometers of recently cleared forests. The destruction, they said, had to stop.

In response, major soy companies in the region reached a landmark agreement as signatories to the Amazon Soy Moratorium (ASM), pledging not to purchase crops grown on recently cleared land. Deforestation fell in the following years, but no one had measured the moratorium’s aggregate impact.

Now, assistant professor Robert Heilmayr and his colleagues at the University of Wisconsin Madison have quantified the ASM’s effects and documented how it achieved its success. The researchers found that the agreement prevented thousands of square kilometers of deforestation over its first decade. What’s more, the policy did not appear to hamper agricultural growth or push deforestation to other sectors or regions. The study, funded by the Gordon and Betty Moore Foundation and the Norwegian International Climate and Forest Initiative, appears in Nature Food.

“Over one decade the ASM saved 18,000 square kilometers of forest,” said Heilmayr, an environmental economist in the Environmental Studies Program and at the Bren School of Environmental Science & Management. “This is an area bigger than the state of Connecticut.”

Around the same time the Amazon Soy Moratorium was adopted, the Brazilian government was expanding its regulations against deforestation. The policies covered the legal Amazon, a larger administrative area that includes the Amazon biome and parts of the Cerrado biome – a vast region of tropical forest and savannah southwest of the rainforest.