(CNN) -- Santino Sena wades through a knee-deep swamp, snatching up green seeds about the size of ping-pong balls that float on the surface of the water.
"These are Landi seeds," he says. "They pay pretty well. About 20 reais ($12) per kilo."
They're used for reforestation projects in central Brazil where loggers, ranchers and farmers have cleared huge swaths of Amazon rainforest and semi-arid savannah.
Sena was one of many workers hired to help slash and burn land in Mato Gross state to make room for crops on Brazil's agricultural frontier.
But the same government that once encouraged settlers to tear down forests is now requiring landowners to replant thousands of hectares with native trees or be denied access to credit and key markets.
"Most of these seeds are headed to the same land that I helped clear," Sena says.
During seed-collecting season, which lasts six months, he can make more than $15,000.
According to the non-profit group SocioEnvironmental Institute (ISA), there are now 300 workers -- from indigenous families to former illegal loggers -- who make a living collecting seeds.
ISA has identified 214 native species that can be used in reforestation and are kept in refrigerated storerooms. The group trains collectors and then helps them find buyers.
"Before, we had to go to farmers to ask for land for our pilot projects," says ISA coordinator Nicola Costa. "Now it's the opposite. Farmers are looking for us."
ISA became involved in the campaign after indigenous groups from the Xingu Park went to them for help to protect water supplies.
Many tributaries running through the forest had dried up due to wide-spread clear-cutting and they said fertilizers were polluting the water.
"In many villages they began to realize that a simple swim in the river caused rashes," said Ianukula Kaiabisuia, coordinator of Xingu Park.
The high cost of hand-planting native seedlings prompted resistance from many farmers and ranchers, but they worked with ISA to find a cheaper alternative.
Now the same tractors they use to plant soybeans are put to work planting seeds from native trees like Landi, Muruci and Baru.
Amandio Micolino, a small-time rancher, is reforesting river margins as required by law. But he has gone a step further, replanting a big chunk of his 400-hectare ranch.
"I want to leave something for future generations so they know what it was like 50 or 100 years ago," he says.
But Micolino is a rare breed here in Brazil's heartland.
In less than three decades the country has gone from being a food importer to a global breadbasket, exporting everything from soybeans to sugar, beef and orange juice, often at the expense of the environment.
So far, just a tiny fraction of the land that was illegally cleared has been reforested.
But seed collectors like Sena aren't discouraged.
"I wouldn't give this job up for the world," he says. "It gives me such a good feeling to be creating something."