Saving biodiversity is a noble goal, but how much will it cost? And where should the money be spent? These are difficult questions for policymakers. An innovative analysis, published in this week’s issue of Science, lays out a plan for Brazil’s diverse and endangered Atlantic Forest.
“The most important message is that restoration can be targeted in a way that minimizes costs and has a greater likelihood of delivering lasting environmental benefits,” says Toby Gardner, an ecologist at the Stockholm Environment Institute, who was not involved in the new research.
South America’s Atlantic rainforest is a good case study for the challenges of conservation policy. With a great variety of environmental conditions, life has evolved into incredible diversity. But farming, ranching, and urban development have destroyed much of the forest. Less than 8% remains of its original 1.43 million square kilometers that spanned Brazil, Paraguay, and Argentina. Over the years, conservationists have made mostly small-scale attempts to restore the forest.
A group of researchers wanted to figure out how much forest is needed to maintain the integrity of biological communities and their ecological functions. They studied the abundances of 43 species of mammals, 140 species of birds, and 29 species of amphibians in 79 landscapes that ranged from nearly deforested to fully intact.
The team identified an important ecological threshold. When the amount of forest drops below 28.5% of the landscape, the communities started to change. For example, generalist species, such as the opossum Micoreus paraguayanus, which prefer disturbed environments, begin to take over from forest specialists. “It’s a very strong conclusion,” Gardner says. The threshold for maintaining existing community integrity is likely to be different in other places, the authors say. It is likely to be higher in the Amazon and lower in Europe and other developed landscapes where sensitive species have already disappeared.
The researchers say it won’t be feasible to restore all 88% of the 143 million hectares of the Atlantic Forest that has been deforested below the threshold; that goal would require 32 million hectares of replanting, most of it on private land.
The smart approach, they say, would be to focus on restoring landscapes that are still at least 20% forested. Working in landscapes with any less forest cover would become prohibitively expensive and risky, involving translocation of endangered species. But planting trees on 424,000 priority hectares would ensure community integrity in 37,000 landscapes throughout the Atlantic Forest, providing ecosystems services such as pollination of nearby crops and pest control. The amount of land with at least 30% forest cover would increase by 46%. Preventing extinction of species such as the jaguar will require larger protected areas, they note.
By extrapolating from existing forest restoration projects in Brazil, the researchers estimated that restoration of these priority areas would cost about $198 million a year for 3 years. The cost would then decline, as less watering and other work is required. “We can make farmers happy and preserve biodiversity all within a reasonable budget,” says Cristina Banks-Leite, an ecologist at Imperial College London, Silwood Park. Gardner suspects the cost would end up lower, given economies of scale.
“The results are very exciting,” says Bernardo Strassburg, an economist and environmental scientist at the Pontifical Catholic University of Rio de Janeiro in Brazil, who was not involved in the research. “This is one of the first papers to narrow down the effort to the most effective regions and show where they are.”
Banks-Leite and Strassburg both say there’s political will to boost restoration. An existing effort by more than 250 nongovernmental organizations, companies, and government agencies has a target of 15 million hectares restored by 2050. And the federal government is expected to launch a national restoration strategy in a few months.
Pedro Brancalion, a restoration ecologist at the University of São Paulo in Brazil, says it will be important to make sure that turning pasture back to forest doesn’t encourage cattle ranchers to cut down forest elsewhere. “We have to integrate agricultural intensification,” he says. “If we have minimum input of technology, we could save millions of hectares.”