The spread of crops beyond their centers of domestication represents among the most abrupt and expansive changes to biogeography throughout Earth’s history, and represents a central line of evidence supporting the “Anthropocene Epoch” hypothesis. At continental scales, the past 60 years have seen pronounced increases in the diversity of plant crops being grown on large-scale agricultural lands. Yet at a global scale, these changes have contributed to increasing homogeneity of croplands worldwide, as four crops (soy, maize, wheat, and rice) have come to dominate ~50% of Earth’s agricultural lands. Crop diversity change has been documented at global and continental scales, yet remains unclear how crop diversity change has unfolded at a country-scale, where a) the drivers of crop diversity change differ widely, and b) changes in crop diversity are likely to have detectable impacts on ecological functions such as biogeochemical cycling. We used open-access data from the United Nation’s Food and Agricultural Organisation (FAO) documenting the area cultivated for 156 crop commodity groups and 339 crop species, in order to 1) assess how crop taxonomic diversity has changed across 221 countries over the past six decades (from 1961 to 2017), and 2) evaluate the environmental drivers and consequences of these changes.
Results/Conclusions
Since 1961 the large majority of countries (195) worldwide have experienced pronounced increases in crop diversity (measured as crop species richness), with only a small number of countries (6) experiencing evidence of diversity declines. The most prominent period of diversity change occurred throughout the mid-1980s, with crop diversification commencing in 1986 on average and continuing for ~1 decade. However, the timing and duration of these changes differs widely across countries. Cluster and multivariate analyses further indicate that the mid-1980s marks a time where the composition of countries’ agricultural lands shift drastically. Specifically, while country-level crop diversity generally increases during the 1980s, this also marks a time where countries become markedly more similar in their crop composition. Country-scale changes in crop diversity were only weakly associated with environmental and land-use change, instead suggesting socio-economic factors are more likely driving patterns. Yet stronger links between crop composition and certain environmental indicators (namely, nitrogen-based fertilizer applications) suggest these changes have a pronounced impact on large-scale biogeochemical processes.