RIO CLARO, BRAZIL (AP) - The cash cows on Carlos Marques' farm used to be nothing but that: herds of dairy cattle that grazed the grassy, rolling hills of his property, where most of the dense tropical forest was long ago cut down for pastures and cropland.
But now the trees are starting to put money in his pocket as well.
The 68-year-old farmer is part of a pilot project that aims to reverse the economics of environmental destruction by paying farmers to preserve the forests that protect a crucial watershed, using money from some of the millions of people who use that water.
It's the sort of initiative that is at the heart of the United Nations' Rio+20 earth summit, the three-day mega-conference that ends Friday and is aimed at pushing sustainable development to the top of the world's agenda.
"It used to be that the forest was worth nothing," said Fernando Veiga, water funds manager at The Nature Conservancy, the environmental organization that helped spearhead the Rio Claro-area project along with a Brazilian NGO and the state and municipal governments. "But we know how crucial living trees are to the planet, and now they have a monetary value."
Proponents insist that sustainable development _ which allows economic growth to meet people's current needs while preserving natural resources for the future _ is the only way to prevent an environmental meltdown that could prove catastrophic for the planet and humanity.
But critics contend that the idea often serves as a front that permits governments and companies to make noise about protecting the environment while permitting business to continue as usual.
Looking out onto rounded hills that surround Marques' farm near the tiny town of Rio Claro, 130 kilometers (80 miles) south of Rio de Janeiro, it's hard to believe this entire region was once swathed in dense vegetation. Devastated by centuries of deforestation _ first for coffee plantations, then for charcoal and now for cattle raising and urban sprawl _ Brazil's Atlantic Forest has been whittled down to just 12 percent of its original size, and scientists say it ranks among the world's most threatened ecosystems.
The hills around Rio Claro are now almost bald, with just a sparse covering of grass that's often chewed down to the root by the rangy cattle that graze here. With little to anchor the earth into place, erosion has cut vivid gashes of rusty red soil.
This desolate landscape is the source for the Guandu River, which provides 80 percent of Rio's water. Because of deforestation and erosion, water is less abundant than locals say it once was, and silt from the erosion and other pollutants seep into the tributaries of the Guandu, as well as the river itself. That forces water officials to heavily treat the water to make it usable, costing the city $500 million per year, according to environmentalists. And still, most Rio residents who can afford it drink bottled water.
On Marques' property, for example, the brook that once babbled its way across his land had dried up, as have many other other streams in the area, the farmer said.
The Nature Conservancy and partner organization Instituto Terra developed the Guandu Water Fund to protect Rio's water supply by investing in the forests that help generate the water itself.
Under the pilot project, inaugurated in 2009, $500,000 in fees paid by big water consumers are being doled out to small farmers around Rio Claro who pledge to conserve their forests or allow swaths of their land to be reforested.
Farmers sign a contract promising to keep their animals out of protected plots, and organizers send out teams of locally hired employees to fence in the areas and plant thousands of saplings from a potpourri of some 80 native plant species.
The payouts are mostly small _ Marques receives just $640 a year for his 62 protected acres _ but advocates say even symbolic amounts help change people's attitudes toward conservation.
"I used to think of the trees as mine, to use as I saw fit, but now I see things differently," said Marques, a father of five and grandfather of five. "The trees that grow here are mine, but lots of other people depend on them, too, so by saving even just one single tree, I'm performing a service for all of humanity."
Since he joined the project three years ago, the dried-up stream has been resuscitated. At first it was a mere trickle, he said, but now it's grown into a thick rope of water.
With real, measurable gains for 9 million consumers in Rio de Janeiro, for the forest and for the locals who call it their home, the Guandu Water Fund embodies the win-win situation for people and the environment that sustainable development aspires to be.
Such initiatives are gaining traction among policymakers as a way to slow the kind of wholesale environmental destruction that has been blamed for recent years' rise in devastating droughts, floods and other natural disasters.
The notion of sustainable development was born well ahead of the current conference's precursor, the U.N.'s 1992 Earth Summit, which helped put climate change on the world agenda. Still, it remains an amorphous, and divisive, concept.
"Definitions of just what is sustainable development vary, society by society," said Jeffrey Sachs, the economist and who heads Columbia University's Earth Institute. "But while there are big debates about the specifics and how to balance ... the economy, the environmental and the social concern, I think that the basic idea that we have three bottom lines, not one, is the most important idea."
Still, it has been hard to agree on how to implement it.
Weeks of bickering between rich and poor countries delayed agreement on the final summit conclusions and the result has disappointed environmental groups, who have lambasted it as toothless and inadequate.
"What most people at the summit are talking about when they talk about sustainable development is nothing but business as usual under a different name, something that will deliver misery to many and profit to a few," said Daniel Mittler, a political director at Greenpeace who is heading the environmental group's delegation at Rio+20.
"But it doesn't have to be: Sustainability is an agenda that can deliver for people and the planet at the same time," Mittler said, adding that political will and direction are needed to make it work on a global scale. "The tragedy of Rio+20 is that governments are failing to grasp that opportunity."
While decision makers squabble over language, farmer Marques in Rio Claro says he's sold on sustainable development.
"I need money to live, but I also need clean air and clean water," he said. "This project gives me all three at the same time."