美国农场农作物多样性下降

U.S. farmers are growing fewer types of crops than they were 34 years ago, which could have implications for how farms fare as changes to the climate evolve, according to a large-scale study by Kansas State University, North Dakota State University and the U.S. Department of Agriculture. Less crop diversity may also be impacting the general ecosystem. "At the national level, crop diversity declined over the period we analyzed," said Jonathan Aguilar, K-State water resources engineer and lead researcher on the study.

The scientists used data from the USDA's U.S. Census of Agriculture, which is published every five years from information provided by U.S. farmers. The team studied data from 1978 through 2012 across the country's contiguous states.

Croplands comprise about 408 million acres (165 million hectares) or 22 percent of the total land base in the lower 48 states, so changes in crop species diversity could have a substantial impact, not only on agroecosystem function, but also the function of surrounding natural and urban areas. Because croplands are typically replanted annually, theoretically crop species diversity can change fairly rapidly. There is the potential for swift positive change, unlike in natural ecosystems.

Aguilar began the study while working as a researcher with the USDA's Agricultural Research Service. He joined K-State Research and Extension, a part of the university, in 2012. The study was conducted in collaboration with a diverse team, including rangelands expert John Hendrickson, USDA-ARS; weeds experts Greta Gramig, NDSU, and Frank Forcella, USDA-ARS; agricultural economics expert David Archer, USDA-ARS; and soils expert Mark Liebig, USDA-ARS. 

"At the very simplistic level," Aguilar said, "crop diversity is a measure of how many crops in an area could possibly work together to resist, address and adjust to potential widespread crop failures, including natural problems such as pests and diseases, weed pressures, droughts and flood events. This could also be viewed as a way to spread potential risks to a producer. Just like in the natural landscape, areas with high diversity tend to be more resilient to external pressures than are areas with low diversity. In other words, diversity provides stability in an area to assure food sustainability."