Whether conservation initiatives, such as protected forest areas, help bring local people out of poverty is hotly debated. For example, some researchers argue that protecting ecosystems limits agricultural development of the land and stops local people from exploiting natural resources in those areas.

Studies on the topic have produced mixed results. But much of the research has failed to pin down a link between conservation and poverty reduction because they don’t use appropriate controls.

A study published today in the Proceedings of the National Academy of Science takes a more robust approach. The research looked at communities living near protected areas that are 15 or more years old in both Thailand and in Costa Rica. It tracked communities’ state of poverty from levels in 2000 and compared it to similar populations living in areas that were not protected.

The proportion of people living in poverty in protected areas dropped by 30% compared to people in non-protected areas in Thailand, the study found.

And in Costa Rica, the study was able to attribute 10 % of the poverty reduction seen in populations living in protected areas to the conservation initiative.

But the research was unable to say how protected areas helped poor people. For example, local communities may have benefited through a number of routes including an increase in the value of ecosystem services, forest tourism, or through infrastructure development.

“We have shown a causal link between protected areas and poverty alleviation. But we don’t know what the mechanisms are,” says Paul Ferraro, an economist at Georgia State University, Atlanta, and co-author of the research.