With the global population rising, analysts and policymakers have proposed Africa’s vast wet savannas as a potential place to produce staple foods and bioenergy crops at low environmental costs. But a report published by Princeton researchers finds that converting Africa’s wet savannas into farmland would come with high environmental tradeoffs.

“Many papers and policymakers have simply assumed that Africa’s wetter savannas are expendable from an environmental standpoint because they aren’t forests,” said co-lead author Tim Searchinger, a research scholar at the Center for Policy Research on Energy and the Environment. However, after calculating the carbon and biodiversity losses that would result from the ecological conversion to cropland, the results are far less environmentally beneficial than previously believed.

The study finds that only a small percentage of Africa’s wet savannas have the potential to produce staple crops while emitting significantly less carbon dioxide than the world’s average cropland. In addition, taking land conversion into account, less than 1% of these lands would produce biofuels that meet European standards for greenhouse-gas reductions.

The results highlight the need for policies that manage where and to what extent cropland expansion occurs.