Mar 27, 2008
Climate Change May Be Fueling Weed GrowthSource: Weed Science Society of America

As if we needed another reason to worry about the effects of global warming, recent research points a finger at global warming as the possible culprit behind a new generation of more aggressive weeds.

According to a press release by the Weed Science Society of America, one of the major characteristics of a warming planet is an increase in the amount of carbon dioxide in the atmosphere. Rising carbon dioxide has been shown to help vegetable and grain crops grow more quickly, become more drought resistant and produce potentially higher yields. However, the impact of rising carbon dioxide seems to be far more pronounced in the weeds that compete with crops than in the crops themselves.

“Weeds are survivors,” said Lee Van Wychen, director of science policy for the society, in a press release. “They can fill various niches and thrive under a wide range of conditions.”

While there are about 45 major crops in the United States, there are more than 400 species of different weeds associated with those crops. “There is always another weed species ready to become a major competitor with a crop if growing conditions change, such as an increase in carbon dioxide levels,” Wychen added.

In fact, the impact of rising carbon dioxide levels on weeds can be “striking” , according to the press release. In a study conducted by Dr. Lewis Ziska of the U.S. Department of Agriculture’s Agricultural Research Service, weeds grown under urban conditions of warmer temperatures and more carbon dioxide – conditions anticipated for the rest of the world in 50 years – grew to four times the height of those in a country plot 40 miles outside the city, where carbon dioxide levels and temperature reflected background conditions.

Ziska’s research shows that common ragweed plants exposed to higher levels of carbon dioxide dramatically increased the amount of pollen they produced. Some people are allergic to ragweed pollen, resulting in “hay fever” response, including sneezing and watery eyes.

Additional work by Ziska suggests that even recent increases in carbon dioxide during the last 50 years may have led to bigger poison ivy plants with a more virulent form of the oil that causes people to break out in a rash.

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