Unexpectedly large impact of forest management and grazing on global vegetation biomass

Abstract

Carbon stocks in vegetation have a key role in the climate system1,2,3,4. However, the magnitude, patterns and uncertainties of carbon stocks and the effect of land use on the stocks remain poorly quantified. Here we show, using state-of-the-art datasets, that vegetation currently stores around 450 petagrams of carbon. In the hypothetical absence of land use, potential vegetation would store around 916 petagrams of carbon, under current climate conditions. This difference highlights the massive effect of land use on biomass stocks. Deforestation and other land-cover changes are responsible for 53–58% of the difference between current and potential biomass stocks. Land management effects (the biomass stock changes induced by land use within the same land cover) contribute 42–47%, but have been underestimated in the literature. Therefore, avoiding deforestation is necessary but not sufficient for mitigation of climate change. Our results imply that trade-offs exist between conserving carbon stocks on managed land and raising the contribution of biomass to raw material and energy supply for the mitigation of climate change. Efforts to raise biomass stocks are currently verifiable only in temperate forests, where their potential is limited. By contrast, large uncertainties hinder verification in the tropical forest, where the largest potential is located, pointing to challenges for the upcoming stocktaking exercises under the Paris agreement.

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Figure 1: Differences in biomass stocks of potential and actual vegetation induced by land use.
Figure 2: Contribution of land-use types to the difference between potential and actual biomass stocks.
Figure 3: Uncertainty of biomass stock estimates.

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Acknowledgements

Funding from the European Research Council (ERC-2010-stg-263522 ‘LUISE’), the European Commission (H2020-EO-2014-640176 ‘BACI’), the German Research Foundation’s Emmy Noether Program (PO 1751/1-1), GlobBiomass project of the European Space Agency (4000113100/14/I-NB), the NOVA grant UID/AMB/04085/2013, the Amsterdam Academic Alliance (AAA) and the Vetenskapsrådet grant 621-2014-4266 of the Swedish Research Council are acknowledged. We thank A. Baccini, A. S. Ruesch, S. Saatchi and P. C. West for making their data layers publicly available. K.H.-E. is grateful for the support by K. Kowalski. This research contributes to the Global Land Programme (https://glp.earth/).

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K.-H.E., T.K., C.P. and S.L. designed the study and performed the research, A.L.S.B., N.C., T.F., S.G., H.H., C.L., M.N., M.T. and J. P. contributed and analysed data and results, and all authors contributed substantially to the analysis, interpretation of results and writing of the manuscript.

Corresponding author

Correspondence to Karl-Heinz Erb.

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Reviewer Information Nature thanks A. Friend, R. Houghton and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Figure 1 Estimates of the potential and actual biomass stocks from the literature and this study.

a, Potential biomass stocks. b, Actual biomass stocks. Datasets from the following studies were used: (1)69, (2)3, (3)70, (4)54, (5)20, (6)71, (7)72, (8)73, (9)56, (10)74, (11)75, (12)76, (13)77, (14)78, (15)79, (16)48, (17)80, (18)81 (19)72. The darker shaded columns are those used in this study (for details see text). Source data

Extended Data Figure 2 Conceptual and methodological design of the study.

a, The relation of prehistoric (α), potential (β) and actual (γ) biomass stocks. Potential vegetation refers to the vegetation that would prevail in the absence of land use but with current environmental conditions. As both actual and potential vegetation refer to the same environmental conditions, their difference must not be interpreted as a stock change between two points in time. As a consequence, the comparison of potential and actual biomass stocks does not refer to the cumulative net balance of all fluxes from and to the biomass compartment (for example, induced by land-use and environmental changes). Rather, it isolates and quantifies the effect of land use on biomass stocks. The effect of land use consists of two components, that is, cumulative land-use emissions and land-use-induced reductions in carbon sequestration that would result from environmental changes. For more information and discussion, see Supplementary Information. b, Conceptual attribution of the difference between potential and actual biomass stocks to land conversion and land management. Error bars reflect the divergence among datasets for the respective vegetation types and indicate the determination of verification volumes.

Extended Data Figure 3 Actual biomass stock maps used in the study.

a, FRA-based map. bd, Maps based on refs 16 (b), 6 and 8 (c), and 7 and 8 (d). e, Remote-sensing-derived minimum. f, Remote-sensing-derived maximum. g, Map from ref. 48. The same mask for unproductive areas has been applied to all maps. For details and sources of maps in af, see Methods.

Extended Data Figure 4 Potential biomass stock maps used in the study.

a, IPCC-based, FRA-adjusted map. b, IPCC-based map adjusted using data from ref. 16. c, Cell-based minima of classic data. d, Cell-based maxima of classic data. e, Remote-sensing-derived map. f, Map from ref. 56. The same mask for unproductive areas has been applied to all maps. For details and sources for maps in ae, see Methods.

Extended Data Figure 5 Land-use-induced difference in potential and actual biomass stocks, uncertainty of input data and vegetation units used in the study.

a, Impact of land-cover conversion. b, Impact of land management. a, b, Maps are based on the FRA-based actual biomass-stock map and the corresponding, IPCC-based FRA-adjusted potential carbon-stock map. c, Standard deviation of potential biomass-stock maps (n = 6). d, Standard deviation of actual biomass-stock maps (n = 7). e, Intersect of all three37,38,39 biome maps used in the ecozone approaches and for the construction of the remote-sensing-based potential biomass-stock map. f, FAO ecozones37 used for the aggregation of results. The ‘tropical core’ consists of humid rainforests. The tropical zones contain moist deciduous forests, dry forests, tropical shrubs, savannahs and hot deserts.

Extended Data Table 1 Biomass stocks per type of land use
Extended Data Table 2 Compilation of published estimates of emissions associated with anthropogenic land-cover change and land management until present (industrial and pre-industrial)
Extended Data Table 3 Comparison of the difference between potential and actual biomass stocks to components of the global carbon balance, including land-use change (LUC) emissions and net terrestrial biosphere sink
Extended Data Table 4 Hypothetical absorption potentials of carbon stock restorations and indicative years until saturation at a current emission level of 9 PgC yr−1

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Supplementary Information

This file contains supporting text “Contextualizing the difference of potential and actual carbon stocks with global carbon balance accounts”, supporting tables 1-3 and additional literature. (PDF 755 kb)

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Erb, K., Kastner, T., Plutzar, C. et al. Unexpectedly large impact of forest management and grazing on global vegetation biomass. Nature 553, 73–76 (2018). https://doi.org/10.1038/nature25138

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