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# Crop asynchrony stabilizes food production

Delphine Renard, David Tilman

► To cite this version:

Delphine Renard, David Tilman. Crop asynchrony stabilizes food production. Nature, 2020, 588 (7837), pp.E13-E13. 10.1038/s41586-020-2965-6. hal-04910460

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https://hal.science/hal-04910460v1

Submitted on 20 Feb 2025

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# Reply to: Crop asynchrony stabilizes food production

Renard D, Tilman D

¹CEFE, CNRS, Univ. Montpellier, University Paul Valéry Montpellier 3, EPHE, IRD, Montpellier, France. ²Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara, CA, USA. ³Department of Ecology, Evolution and Behavior, University of Minnesota, St Paul, MN, USA. ⁴e-mail: delphinerenard@hotmail.fr

REPLYING TO L. Egli et al. Nature https://doi.org/10.1038/s41586-020-2965-6 (2020)

In the accompanying Comment, Egli et al.¹ report findings related to our Article² on the stabilization of food production by crop diversity. In our Article, we reported that crop diversity stabilized the combined caloric yield of all crops in a nation². Our analyses showed that the portfolio effect³ was the probable cause of this greater stability, and we found no support for the asynchrony hypothesis⁴. Egli et al.¹ report somewhat different findings.

The results in our Article² differ from those of Egli et al.¹ because we analysed the year-to-year temporal stability of national caloric yield for all crops combined and analysed for asynchrony among individual crops using the national yield of each crop. By contrast, Egli et al.¹ analysed the stability of total national caloric production and measured asynchrony on the basis of the annual national caloric production of each individual crop. Although yield and production are related to each other, they are not identical. Yield is the crop production per unit of land, whereas production is the yield multiplied by the cropland area. Even using their different metric, Egli et al.¹ found—as did we—that greater crop diversity led to greater national temporal crop stability.

We suggest that national yield stability is the more informative and insightful of these two stability metrics because it directly measures the year-to-year reliability of food production from a typical hectare of cropland in a nation. If the total area planted and harvested had been constant from 1961 until now in each nation, the two measures of stability would be identical. However, harvested area has been increasing in many lower-income nations for the past 60 years (an increase of 69% in the least-developed nations since the 1960s⁵), and it first increased and then declined in many high-income nations (a decrease of 29% in Europe since the 1980s⁵). These year-to-year changes in total national cropland area and year-to-year changes in yields both affect the stability metric used by Egli et al.¹. Because the database of the Food and Agriculture Organization of the United Nations (FAOSTAT) reports the area harvested for each crop, not the area planted, the potential to determine the effects of changes in area planted on national food supply stability is limited. Finally, because yield stability is independent of year-to-year changes in national cropland area, we feel that yield stability is more informative of underlying biological mechanisms than is production stability. However, when more detailed data are available, assessing changes and drivers of stability of yield and cropland area would be informative. We have similar concerns about the measure of asynchrony used by Egli et al.¹. To calculate asynchrony, they used data on the annual country-level production of each crop, rather than the annual country-level yields that we used. Their metric of asynchrony therefore confounds fluctuations in the performance of individual crops—as measured by yields—with fluctuations in the area planted to, and harvested for, each of these crops, just as does their stability metric.

Because both yields and harvested area affect the total food supply of a country, both have important implications for the agricultural policy of a country. We suggest that viewing each of these separately might be better for providing insights into the best way to maximize the year-to-year stability of food production.
year reliability of the food supply of a country. The link found by Egli et al.¹ between production asynchrony and total crop production stability suggests the possibility that asynchronous variation in area planted with and harvested for various crops might also contribute to national food stability. This interesting possibility merits further exploration.

1. Egli, L., Schröter, M., Scherber, C., Tscharntke, T. & Seppelt, R. Crop asynchrony stabilizes food production. *Nature* https://doi.org/10.1038/s41586-020-2965-6 (2020).

2. Renard, D. & Tilman, D. National food production stabilized by crop diversity. *Nature* 571, 257–260 (2019).

3. Doak, D. F. et al. The statistical inevitability of stability–diversity relationships in community ecology. *Am. Nat.* 151, 264–276 (1998).

4. Loreau, M. & De Mazancourt, C. Species asynchrony and its drivers: neutral and nonneutral community dynamics in fluctuating environments. *Am. Nat.* 172, E48–E66 (2008).

5. *The Food and Agriculture Organization of the United Nations Statistics* (FAO, accessed January 2019); https://www.fao.org/faostat/en/#data/.

Acknowledgements We thank the Bren School of Environment Science and Management of the University of California Santa Barbara for support leading to the initial publication. This work was also supported by a grant overseen by the French ‘Programme Investissement d’Avenir’ as part of the ‘Make Our Planet Great Again’ programme (reference: 17-MPGA-0004) and by a National Science Foundation grant (LTER-1831944).

Author contributions D.R. and D.T. wrote the paper.

Competing interests The authors declare no competing interests.

Additional information

Correspondence and requests for materials should be addressed to D.R.

delphinerenard@hotmail.fr