Lauren Persha and Arun Agrawal of the University of Michigan and Ashwini Chhatre of the University of Illinois used evidence from more than 80 forest sites in six tropical countries in East Africa and South Asia to test how local participation affects social and ecological benefits from forests.

The social benefits include access to forest products that households rely on for their subsistence, such as firewood, fodder for livestock and timber for housing. The main ecological benefit is higher biodiversity in the tropical forests.

"There are substantial disagreements among scientists about whether it's possible to achieve both economic and ecological benefits together from forests, but little work to understand conditions that might lead to this," says Persha, lead author of a Science paper. "Our study is one of very few that has been able to do this kind of analysis in a systematic way across a large number of cases and countries."

Persha and her colleagues analysed patterns of biodiversity conservation and forest-based household livelihoods at 84 study sites. Tree species richness was used as the indicator of forest biodiversity.

The percentage of households that depend significantly on a forest for subsistence livelihoods was used as an indicator of the forest's livelihood contributions. A sustainable forest system was defined as one in which both tree species richness and livelihood contributions were above average.

The researchers found that most cases were a mixed bag, where either tree species richness or livelihood dependence were below average. But in 27% of the cases, both biodiversity levels and livelihood dependence were above average, meeting the criteria for a sustainable forest.

In determining which factors helped to explain these outcomes, the analysis showed that forests are significantly more likely to be sustainable when local users have a formally recognized right to participate in forest rulemaking, while unsustainable forests are more likely when users do not have this right.

"It's a lesson for governments about how to make policies to manage and govern their forests," says Agrawal.

The authors state that their findings are particularly relevant for small forest patches in regions with high population density – instances that present special challenges for achieving sustainability.

Hundreds of millions of people in the tropics depend on forests. In recent years, governments in nearly two-thirds of the developing world have tried to involve rural households and organizations in forest management. Often, the goal is to improve both social and ecological results by giving local residents incentives to manage forests sustainably.

Such reforms have doubled the area of forest land under community management in the past 15 years. But experts disagree over whether allowing local people to participate in forest rulemaking improves forests or leaves them worse off – and most studies do not examine the effects of this practice.

"These disagreements have persisted for decades because the evidence needed to resolve them simply didn't exist," Agrawal says. "The current study is an important step toward improved evidence and analysis on this subject."