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1. Increasing landscape heterogeneity by restoring semi-natural elements to reverse farmland biodiversity declines is not always economically feasible or acceptable to farmers due to competition for land. We hypothesized that increasing the hetero-geneity of the crop mosaic itself, hereafter referred to as crop heterogeneity, can have beneficial effects on within-field plant diversity .2. Using a unique multi-country dataset from a cross-continent collaborative project covering 1,451 agricultural fields within 432 landscapes in Europe and Canada, we assessed the relative effects of compositional and configurational crop heteroge-neity on within-field plant diversity components. We also examined how these relationships were modulated by the position within the field. 3. We found strong positive effects of configurational crop heterogeneity on within-field plant alpha and gamma diversity in field interiors. These effects were as high as the effect of semi-natural cover. In field borders, effects of crop heterogeneity were limited to alpha diversity. We suggest that a heterogeneous crop mosaic may overcome the high negative impact of management practices on plant diversity in field interiors, whereas in field borders, where plant diversity is already high, landscape effects are more limited. 4. Synthesis and applications. Our study shows that increasing configurational crop heterogeneity is beneficial to within-field plant diversity. It opens up a new effec-tive and complementary way to promote farmland biodiversity without taking land out of agricultural production. We therefore recommend adopting manipulation of crop heterogeneity as a specific, effective management option in future policy measures, perhaps adding to agri-environment schemes, to contribute to the con-servation of farmland plant diversity. ; Natural Sciences and Engineering Research Council of Canada; German Ministry of Research and Education; Agence Nationale de la Recherche, Grant/Award Number: ANR-11-EBID-0004; Canada Foundation for Innovation; German Research Foundation; Spanish Ministry of Economy and Competitiveness; Agriculture and Agri-Food Canada; French National Research Agency, Grant/Award Number: ANR-11-EBID-0004; UK Government Department of the Environment, Food and Rural Affairs; Environment Canada (EC)

Agricultural landscape homogenization has detrimental effects on biodiversity and key ecosystem services. Increasing agricultural landscape heterogeneity by increasing seminatural cover can help to mitigate biodiversity loss. However, the amount of seminatural cover is generally low and difficult to increase in many intensively managed agricultural landscapes. We hypothesized that increasing the heterogeneity of the crop mosaic itself (hereafter "crop heterogeneity") can also have positive effects on biodiversity. In 8 contrasting regions of Europe and North America, we selected 435 landscapes along independent gradients of crop diversity and mean field size. Within each landscape, we selected 3 sampling sites in 1, 2, or 3 crop types. We sampled 7 taxa (plants, bees, butterflies, hoverflies, carabids, spiders, and birds) and calculated a synthetic index of multitrophic diversity at the landscape level. Increasing crop heterogeneity was more beneficial for multitrophic diversity than increasing seminatural cover. For instance, the effect of decreasing mean field size from 5 to 2.8 ha was as strong as the effect of increasing seminatural cover from 0.5 to 11%. Decreasing mean field size benefited multitrophic diversity even in the absence of seminatural vegetation between fields. Increasing the number of crop types sampled had a positive effect on landscape-level multitrophic diversity. However, the effect of increasing crop diversity in the landscape surrounding fields sampled depended on the amount of seminatural cover. Our study provides large-scale, multitrophic, cross-regional evidence that increasing crop heterogeneity can be an effective way to increase biodiversity in agricultural landscapes without taking land out of agricultural production. ; This research was funded by the ERA-Net BiodivERsA, with the national funders French National Research Agency (ANR-11-EBID-0004), German Ministry of Research and Education, German Research Foundation and Spanish Ministry of Economy and Competitiveness, part of the 2011 BiodivERsA call for research proposals. The UK component of this research was funded by the UK Government Department of the Environment, Food and Rural Affairs (Defra), as Project WC1034. The Canadian component of this research was funded by a Natural Sciences and Engineering Research Council of Canada Strategic Project, the Canada Foundation for Innovation, Environment Canada, and Agriculture and Agri-Food Canada. N.G. was supported by the AgreenSkills+ Fellowship programme which has received funding from the EU's Seventh Framework Programme under Grant Agreement FP7-609398 (AgreenSkills+ contract). A.G.-T. (Juan de la Cierva Fellow, JCI-2012-12089) was funded by Ministerio de Economía y Competitividad (Spain). C. Violle was supported by the European Research Council Starting Grant Project "Ecophysiological and biophysical constraints on domestication of crop plants" (Grant ERC-StG-2014-639706-CONSTRAINTS). A.R.'s position at the University of Alicante is funded by the "Vicerrectorado de Investigación y Transferencia de Conocimiento."