Abstract
Land cover data are commonly used to model the terrestrial carbon (C) sink, yet these data have wide margins of error that significantly alter estimates of global C storage. Here we demonstrate this data vulnerability in grasslands, which are critical to C cycling but whose estimated distribution has varied by >50 million km2 (3.5–42% of the Earth’s terrestrial surface). Comparing multiple high-resolution land cover products with expertly annotated grassland data from six continents, we show sources of mapping error and discuss C implications based on 2023 United Nations (UN) FAO estimates. Past misidentification arose from inconsistent definitions on grassland identity and classification flaws especially relating to woody plant cover. Correcting these errors adjusted grassland coverage to 22.8% of the terrestrial land base (30.1 million km2), elevating UN projections of soil C stocks to 155.02 Pg (0–30 cm depth). These findings underscore the challenges of biome mapping for ecosystem accounting and policy, when lacking field-validated remotely sensed data.
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All data and materials used in the analysis are available from the corresponding authors on request.
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Acknowledgements
We thank each of the researchers who have contributed data and ideas to this paper. This study was largely funded by the Canada First Research Excellence Fund—University of Guelph (‘Food from Thought’), with support from the Natural Sciences and Engineering Research Council of Canada (A.S.M.). M.B.S. acknowledges funding from the Swedish Research Council (2021-05767), FORMAS (2020-01073) and the European Union’s Horizon Program project ILLUQ (no. 101133587). Funding was also provided to E.W.S. and E.T.B. by the National Science Foundation Research Coordination Network (NSF-DEB-1042132) and the Long-Term Ecological Research (NSF-DEB-1234162 to Cedar Creek LTER) programmes, and the Institute on the Environment (DG-0001-13). Y.M.B. acknowledges financial support from Research Ireland, Northern Ireland’s Department of Agriculture, Environment and Rural Affairs (DAERA), UK Research and Innovation (UKRI) via the International Science Partnerships Fund (ISPF) under grant number [22/CC/11103] at the Co-Centre for Climate + Biodiversity + Water. N.E. was supported by the German Centre for Integrative Biodiversity Research (iDiv), Halle-Jena-Leipzig iDiv funded by the German Research Foundation (DFG– FZT 118, 202548816), and funding by the DFG (Ei 862/29-1). S.C.P. acknowledges funding from NSF OCE-1832178.
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A.S.M., M.B.S., J.S. and B.V., with D.N., S. Bagchi and T.O.M., conceptualized the project. B.V., with A.S.M. and M.B.S., designed the methodology. B.V., with A.S.M., M.B.S. and J.S., conducted the investigations. All authors gathered the data. B.V., with A.S.M., M.B.S. and J.S., performed the visualization. A.S.M., with M.B.S., acquired the funding. A.S.M., with M.B.S., J.S., S. Bagchi, D.N. and T.O.M., administered the project. A.S.M., with M.B.S. and J.S., supervised the project. A.S.M., with B.V., M.B.S., J.S., E.W.S. and E.T.B., wrote the original draft of the paper. All authors reviewed and edited the paper.
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MacDougall, A.S., Vanzant, B., Sulik, J. et al. The global extent of the grassland biome and implications for the terrestrial carbon sink. Nat Ecol Evol (2026). https://doi.org/10.1038/s41559-025-02955-6
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DOI: https://doi.org/10.1038/s41559-025-02955-6
