Counting the cost of farming Africa’s ‘wet savannahs’

Farming Africa’s wet savannahs to meet global demands for food and bioenergy could have high carbon and biodiversity costs, according to a paper published online in Nature Climate Change. These findings contrast with studies that assumed these lands could be converted to cropland with relatively low environmental impact.

Previous studies, for example by the Food and Agriculture Organization of the United Nations, have implicitly identified African savannahs and shrublands as potential areas for cropland expansion, however the effects of land conversion on carbon emissions and biodiversity are not well understood.

Timothy Searchinger and colleagues modelled the carbon and biodiversity cost of farming a wide range of ‘suitable’ (having sufficient soil moisture for agriculture) African savannahs, shrublands and woodlands. They found that only very small proportions of this land area, two to three per cent for maize and 10 per cent for soybeans, can be converted to high yielding cropland without high carbon costs. Less than one per cent could produce biofuels that would meet European standards for greenhouse gas reductions. The authors also found that the area they studied has similar average bird and mammal diversity to wet tropical forests. The study suggests that policymakers aiming to preserve biodiversity and curb carbon dioxide emissions should not target African wet savannahs for mass expansion of biofuel and food production.

doi: 10.1038/nclimate2584

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