High carbon and biodiversity costs from converting Africa’s wet savannahs to cropland

Abstract

Do the wet savannahs and shrublands of Africa provide a large reserve of potential croplands to produce food staples or bioenergy with low carbon and biodiversity costs? We find that only small percentages of these lands have meaningful potential to be low-carbon sources of maize (2%) or soybeans (9.5–11.5%), meaning that their conversion would release at least one-third less carbon per ton of crop than released on average for the production of those crops on existing croplands. Factoring in land-use change, less than 1% is likely to produce cellulosic ethanol that would meet European standards for greenhouse gas reductions. Biodiversity effects of converting these lands are also likely to be significant as bird and mammal richness is comparable to that of the world’s tropical forest regions. Our findings contrast with influential studies that assume these lands provide a large, low-environmental-cost cropland reserve.

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Figure 1: Cropland and tree cover in Africa’s wet savannahs and shrublands.
Figure 2: Low-carbon potential cropland sites.
Figure 3: Carbon payback times for use of dedicated perennial grasses for ethanol.
Figure 4: Comparison of GS vertebrate diversity with the rest of the world.

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Acknowledgements

The authors wish to thank N. Walker for encouragement and for helping to organize the workshop that gave rise to this paper, and for financial support, the authors wish to thank the Princeton Environmental Institute Development Grand Challenges Program, the David & Lucile Packard Foundation, the Norwegian Agency for Development Cooperation, the Gordon and Betty Moore Foundation, the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) from the CGIAR Fund and associated donors and the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement no 308371.

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T.D.S. wrote the paper and contributed to all analyses. L.E. undertook the biodiversity and land-use analyses and contributed to all other analyses. P.K.T. performed the DSSAT crop modelling. T.B. led the bioenergy analysis and all work involving the LPJmL model. A.N. contributed to land-use analysis and mapping. D.R. contributed to the biodiversity analysis. R.H. carried out bioenergy analysis with the GREET model and food and land-use demand needs in SSA. R.L. performed yield gap analysis. M.H. contributed land-use analysis. All authors contributed to the general paper content, thinking and writing.

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Correspondence to Timothy D. Searchinger or Lyndon Estes.

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The authors declare no competing financial interests.

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Searchinger, T., Estes, L., Thornton, P. et al. High carbon and biodiversity costs from converting Africa’s wet savannahs to cropland. Nature Clim Change 5, 481–486 (2015). https://doi.org/10.1038/nclimate2584

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