ALBUQUERQUE (AP) - Blame global warming if those cows don't have enough to eat.
Gradually warmer nights over the past few decades could spell trouble for ranchers on the plains of Colorado and eastern New Mexico who rely on blue grama grass to feed their cattle during the summer.
Blue grama already is losing out to spring plants better adapted to the climate change, according to research published today in the journal Science.
However, the climate change could benefit farmers who depend on a long growing season, said University of Nebraska biologist Rich Alward, who has been studying the new climate regime.
"There are winners and losers," agreed University of New Mexico biology Professor Jim Gosz.
Blue grama is the key grass for grazing because it thrives in the hot summers of the plains, giving cattle something to eat in July and August, said Cimarron rancher Jeff Cornell.
It goes dormant during dry spells, holding its food value so cattle still have something to eat when there's no rain, he said.
It's possible other species favorable to ranching might find their way into the ecosystem, Alward said. But in times of drought, the loss of blue grama would be noticeable.
Alward and colleagues from Colorado State University have studied grasses on northeastern Colorado prairie land, where annual average temperatures have risen more than 2 degrees Fahrenheit since 1970. Most of that warming came at night, with an increase in the overnight lows.
The scientists found a close relationship between the nighttime temperature change and the loss of blue grama grass to invader species - a shift from the summer grasses to spring plants.
Spring plants still could provide fodder for cattle, but could leave them little to eat in the summer.
The patches of land studied in Colorado represent plant communities that extend south across much of northeastern and east-central New Mexico.
Gosz said the shift that Alward has measured indicates an increase in the growing season.
imaailcrigwaClimate scientists have measured a 1-degree Fahrenheit increase in the global average surface temperature this century.
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