UC Davis

Core Ideas: Field crop diversity in the US peaked between 1940 and 1960. Current levels of field crop diversity are similar to what they were in 1900. Field crop diversity in the Midwest has been very low throughout the past 142 years. Describing spatiotemporal patterns of agricultural biodiversity may be an important step toward better understanding its effect on agroecosystem services. We describe species-level field crop diversity at the national and state level for the United States, using annual survey data for a 142-yr period. National-level field crop diversity was very low around 1870 and peaked around 1960, after which time it began to decline. Many states had their highest levels of diversity between 1940 and 1960, but trends varied strongly among states. In 1900, the states with highest diversity were in the Northeast, but in 2012 the highest diversity was found in California, North Dakota, and the southeastern states. Diversity in the central US Corn Belt was very low throughout the 142-yr period studied. These results show that changes in diversity do not necessarily follow a simple continuous decline when moving from “traditional” to “industrial” agriculture.