Monday, September 3, 2007

As carbon dioxide rises, grasslands may lose out

Climate Ark, via Bloomberg: Rising levels of carbon dioxide are causing shrubs to encroach on grasslands, threatening the loss of grazing grounds for livestock farming, U.S. scientists said. The trend is an "important problem" for ranchers who may face "relatively rapid changes" in the amount of grasslands as a result of gains projected in levels of the gas, called CO2, in the atmosphere, researchers said recently in the Proceedings of the National Academy of Sciences.

U.S. Agriculture Department researchers found that the amount of ground covered by the shrub Artemisia frigida rose 20- fold over 5 years on selected plots of land in Colorado where the team doubled the level of CO2, the report said. "We saw a huge increase in the shrub, and we think this is an example of what's happening elsewhere," said Jack Morgan, the research team's leader. "This makes the land less useful, because the cattle prefer the perennial grasses."

…The experiment incorporated a number of elements not found in nature, such as a sudden doubling of CO2 as opposed to a gradual one and the use of open-top chambers to enclose experimental plant patches. Even so, the results provide "a snapshot of what's going on in the wider world," Morgan said.

"It's happening in a number of these grasslands around the world: It's happening in North America, it's happening in Asia, in south Africa, in Australia," Morgan said. "The whole southwest of the U.S., in southern New Mexico, southwest Texas, into Mexico, those were grasslands in the 19th century. They're now shrublands. That's hundreds of thousands of acres."

…"The rate at which CO2 is increasing now is dramatic, and plants are certainly going to respond," the researcher said. "It's a certainty that ecosystems are changing as a response, and this is a case where it looks like the change involves a switch to a grassland that is going to be less desirable for ranchers and people who stock cattle."

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