With climate change predicted to alter precipitation and raise temperatures in North American grain-growing regions by 3 to 4 degrees Celsius (about 5 to 7 degrees Fahrenheit) by the end of the century, crops in the future will face dramatically different growing conditions than they do today.
But a new study shows that over the last century and a half, North American wheat crops spread into regions with even wider temperature and precipitation differences than will arise over the next century. This analysis suggests it will be possible to adapt to new wheat-growing conditions.
"As global change takes place, adaptation will help solve some of the problems that are created. Scientists and farmers are not going to roll over and not do anything," said economist Alan Olmstead of the University of California, Davis, who carried out the analysis with economist Paul Rhode of the University of Michigan, Ann Arbor. "When we look at how great the adaptations were in the past, it gives us a sense of what might be achieved in the future."
The pair used a county-by-country record of wheat production in North America from 1839 to 2007 to document how wheat-growing conditions changed over time. They found that in 2007 the median annual temperature norm for areas of wheat production was 3.7 degrees Celsius (6.6 degrees Fahrenheit) colder than in 1839, and that average precipitation was halved.
The geographic center of wheat production in 1839 was in eastern Ohio. In 2007, it was in west-central South Dakota, the authors said in their paper, published today in Proceedings of the National Academy of Sciences. Farmers grew 26 times more wheat in the United States in 2009 than in 1939, and 270 times more in Canada.
"Wheat moved much farther west. It moved farther north and it moved into much harsher climates — drier and colder," Rhode said.
The change followed settlers moving into these areas who sought wheat varieties that would grow there.
"With the perspective of hindsight, we might say: 'Everyone knows you can grow wheat in Edmonton or South Dakota.' But they didn't know that in 1839," Olmstead said. "The reason was not because they were fools but because research hadn't taken place and the kinds of varieties that would survive in these places did not exist."
A key breakthrough was the introduction of the Turkey variety of wheat, brought to Kansas in 1873 by German Mennonites growing wheat on the steppes of Russia. This was a winter wheat, which gives higher yields than spring wheat, although winter wheat cannot be grown in the harshest conditions.
Although the researchers use wheat as an example, other crops have seen similar expansions of their range, Almstead said.
Future conditions in wheat-growing regions of North America are projected to be wetter and warmer — more like the original conditions in which wheat was cultivated on the continent. But that doesn't mean farmers can just plant seeds from the wheat varieties grown in the mid-1800s, said Stephen Baenziger of the University of Nebraska, Lincoln.
Modern Turkey-type wheat varieties have yields around three times higher than the original, for example. The older strains are important, though, because they provide the genetic material to start from for breeding modern, higher-yielding varieties, Baenziger said.
Breeders should have enough time to develop new varieties as conditions change. Still, Baenziger points out two concerns.
One is that while an increase in average temperature would be easy enough to breed for, the future may bring more variable conditions. "The part that has most breeders concerned is not the trend; it's the variation around that line," he said.
Varieties better suited to warmer average temperatures may not be able to handle a sudden freeze, for example. "The dustbowl temperatures were average, but it was the extremes that got you," he added.
Baenziger's second concern is for agriculture in other parts of the world as the climate changes. "I'm optimistic about wheat production in the U.S.," he said. " I'm far less optimistic about what it means when it gets hotter and drier in sub-Saharan Africa."
Also, he adds, it is important to continue to maintain collections of seeds and other plant materials that provide diverse genetic material to start from for breeding desirable traits. "We've got to make sure we have the resources available," he said.
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