Nature | Vol 588 | 10 December 2020 | E7 Matters arising Crop asynchrony stabilizes food production Lukas Egli 1,2 ✉ , Matthias Schröter 1 , Christoph Scherber 3,4 , Teja Tscharntke 5,6 & Ralf Seppelt 1,7 ARISING FROM D. Renard & D. Tilman Nature https://doi.org/10.1038/s41586-019-1316-y (2019) Stable agricultural systems are fundamental for the reliability of agri- cultural production and food security. Recently, Renard and Tilman 1 reported that crop diversity, calculated as the exponential value of the Shannon diversity index of harvested areas of 176 crops, stabilizes national food production. Here we show that crop asynchrony—that is, asynchronous production trends between different crops 2 —is an even better predictor of agricultural production stability than is crop diver- sity. Our finding suggests that asynchrony is one important property that can explain why a higher crop diversity supports the stability of national food production, and that it should be considered in strate- gies to stabilize agricultural production through crop diversification. We suggest that, as well as yield stability and crop diversity, two addi- tional aspects should be considered in the discussion of the diversity– stability nexus. First, as well as yield stability, the stability of overall production is another relevant aspect of food security. Second, the actual benefits of crop diversity are not related to harvested areas as such, but to the temporal production patterns of the cultivated crops 2 . We suggest that planting multiple crops stabilizes agricultural pro- duction only if they experience asynchronous production trends—for example, due to distinct responses of the individual crops to climatic, economic and political shocks 3 . Here we use statistical models to test whether crop asynchrony is a better predictor of agricultural produc- tion stability than is crop diversity. We largely used the same datasets as Renard and Tilman 1 (Extended Data Table 1) and derived the same explanatory variables used in their analysis, including effective crop species diversity 4 , irrigation 4 , nitrogen use intensity 4 , warfare 5 , temperature and precipitation instability 6–8 for five ten-year intervals between 1961 and 2010 (see Supplementary Meth- ods for details) to predict the stability of total caloric production 4,9,10 . We additionally calculated synchrony between crop-specific caloric production 2,11,12 , an index bounded between 0 and 1, where 1 indicates full synchrony. Asynchrony was then calculated by subtracting syn- chrony from 1, so that higher values indicate higher asynchrony. We used total production instead of yield stability as the response variable, because this offers additional insights into food security and because it can be directly related to asynchrony (see Supplementary Methods for details). Moreover, total production incorporates the effects of changes in cropland area as a result of planning decisions by farmers and of changes in global market dynamics. First, we investigated the relationship between effective crop species diversity and crop asynchrony and tested if this relationship changed over time, as crop homogenization has occurred during recent dec- ades 13 . To predict crop asynchrony, we used a linear mixed-effects model with random slopes for diversity and random intercepts for time intervals 14 . Second, we investigated how either crop diversity, crop asynchrony or both affect caloric production stability. For this, we constructed the main linear regression model used in Renard and Tilman 1 using production stability as the response variable (see Sup- plementary Methods for details). We then ran two additional regression models, one in which we replaced crop diversity with crop asynchrony and one in which we added crop asynchrony. Crop diversity and crop asynchrony were found to be correlated (Spearman’s ρ = 0.49, P < 0.05; Fig. 1a). However, the positive effect of crop diversity on asynchrony decreased over time (Fig. 1a), as indicated by a better performance of a linear mixed-effects model including time interval (Akaike information criterion (AIC) = −340.22) compared to a linear model including crop diversity only (AIC = −336.88). The positive effect of crop asynchrony on caloric production stability was more than three times the effect of crop diversity (Fig. 1b, Extended Data Table 2). Other predictors showed similar trends, although the effect of nitrogen use intensity, time and temperature instability was stronger in the diversity model, whereas the effect of irrigation was lower and insignificant. Moreover, the explanatory power of the model increased from R 2  = 0.28 in the crop-diversity model to R 2  = 0.60 in the asynchrony model (Extended Data Table 2). In the model that includes both predic- tors, the stabilizing effect of crop asynchrony was even stronger and the effect of crop diversity was negative (Fig. 1b, Extended Data Fig. 1); however, explanatory power increased by only 0.01 (Extended Data Table 2). Although crop diversity and asynchrony were correlated, multicollinearity was not an issue in the combined model (the variance inflation factors were less than 2). Given that crop asynchrony was a strong predictor of caloric production stability, we further explored their relationship in the most recent time interval (2001–2010). The highest national crop asynchronies were mainly observed in South and Southeast Asia, China, Central America and parts of Africa (Fig. 2). Countries within these regions typically showed high production stabil- ity, and all countries with high asynchrony achieved at least medium stability. Countries with high production stability and low-to-medium asynchrony were mainly found in North and South America (Fig. 2). The 29 countries that had low asynchrony and stability—including Russia, Argentina and Australia—contributed more than 11% of the total crop caloric production. Our analysis provides an important extension to the results presented by Renard and Tilman 1 . We found that the relationship between crop diversity and crop asynchrony decreased over time, which is a potential consequence of the increasing homogeneity of global food supplies 13 . Most importantly, we identified asynchrony as one important crop property (or trait) that can explain why a higher crop diversity sup- ports the stability of national food production. Crop diversity as such provides only limited insights into the mechanism that underlies stabil- ity. The benefits of crop diversity depend on the production patterns of the cultivated crops. Therefore, strategies to stabilize agricultural production through crop diversification also need to account for the asynchrony of the crops considered. https://doi.org/10.1038/s41586-020-2965-6 Received: 12 February 2020 Accepted: 30 September 2020 Published online: 9 December 2020 Check for updates 1 UFZ - Helmholtz Centre for Environmental Research, Leipzig, Germany. 2 University of Potsdam, Institute of Biochemistry and Biology, Potsdam, Germany. 3 University of Münster, Institute of Landscape Ecology, Münster, Germany. 4 Centre for Biodiversity Monitoring, Zoological Research Museum Alexander Koenig, Bonn, Germany. 5 University of Göttingen, Agroecology, Department of Crop Sciences, Göttingen, Germany. 6 University of Göttingen, Centre of Biodiversity and Sustainable Land Use (CBL), Göttingen, Germany. 7 Institute of Geoscience and Geography, Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany. ✉ e-mail: lukas.egli@ufz.de