Résumé
Increasing global food demand, low grain reserves and climatechange threaten the stability of food systems on national to globalscales. Policies to increase yields, irrigation and tolerance of cropsto drought have been proposed as stability-enhancing solutions.Here we evaluate a complementary possibility—that greaterdiversity of crops at the national level may increase the year-to-yearstability of the total national harvest of all crops combined. We testthis crop diversity–stability hypothesis using 5 decades of data onannual yields of 176 crop species in 91 nations. We find that greatereffective diversity of crops at the national level is associated withincreased temporal stability of total national harvest. Crop diversityhas stabilizing effects that are similar in magnitude to the observeddestabilizing effects of variability in precipitation. This greaterstability reflects markedly lower frequencies of years with sharpharvest losses. Diversity effects remained robust after statisticallycontrolling for irrigation, fertilization, precipitation, temperatureand other variables, and are consistent with the variance-scalingcharacteristics of individual crops required by theory for diversityto lead to stability. Ensuring stable food supplies is a challenge thatwill probably require multiple solutions. Our results suggest thatincreasing national effective crop diversity may be an additional wayto address this challenge.