Weeds flourishing in climate of change

Environment: Research notes that higher temperatures and increased greenhouse gases are causing certain noxious plants to thrive.

January 14, 2003|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

Global warming may not only be heating up the Earth, but making people sneeze.

Lewis H. Ziska, a weed expert at the Beltsville Agricultural Research Center, says that ragweed and other noxious plants are thriving because of higher temperatures and more carbon dioxide in the air - conditions often associated with global warming.

Ziska is finding that the changes are improving the health of weeds and other plants grown at monitoring stations he set up at the Maryland Science Center, a West Baltimore park and a Frederick County farm.

Scientists have been studying global warming for years, but its effects on plants are just beginning to be understood.

They fascinate Ziska, who says rising levels of carbon dioxide will encourage dozens of weeds and invasive plants that damage crops, trigger allergies and might contribute to forest fires and loss of pasture. "If you consider that some plants are thriving and may be squeezing out other plants, from a purely ecological standpoint, what's happening is really cool," he said.

Ziska, who will publish a report of his findings this month, has spent the past decade researching how weeds and other plants are handling climatic changes.

He published a study last year reporting that higher levels of carbon dioxide and warmer temperatures boosted ragweed pollen at the science center, compared with pollen counts at the Carrie Murray Nature Center in Leakin Park and a farm in Buckeystown, Frederick County.

Ziska said that from mid-August through mid-September, the science center site was warmer by 3 degrees Fahrenheit than the farm in Buckeystown. The former also had 30 percent more carbon dioxide than the farm site, and three times as much ragweed pollen.

"The ragweed grew faster and was healthier at the city site, where there were more of the conditions associated with global warming," Ziska said.

Dennis Gebhart, who assisted Ziska with the study and whose company, based in Philadelphia, tracks pollen levels for pharmaceutical firms, said ragweed deserves intensive study. It can grow 10 feet tall, often thrives undetected and is so resilient that its seeds can germinate after lying dormant for 40 years, he said.

Dr. Linda B. Ford, a Nebraska allergist and past president of the American Lung Association, said that that ragweed allergies can cause sneezing, a scratchy throat, sinus congestion and watery eyes. Ragweed pollen also can block airways and exacerbates the effects of asthma, an ailment that causes 5,000 deaths in the United States each year.

The number might not sound large, she said, but notes that these deaths "are preventable with treatment."

Ziska's second study, reporting that the climatic changes had the same effects on six invasive plants, will be published this month in the Journal of Experimental Botany.

In both studies, Ziska compared the temperatures and amounts of carbon dioxide in Frederick County with those at the science center in Baltimore. He said he did that because the city's higher temperatures and increased levels of carbon dioxide, from sources that include car exhaust, reflect what the future will bring to the area with global warming.

"We knew that cities act as heat sinks that trap warmer temperatures, and we think the city is a good surrogate for global warming and what it will bring, " Ziska said.

Scientists say Ziska's work is important because weeds have such wide-ranging impact. They not only cause allergies but damage forests and pastures and crowd out crops, costing U.S. farmers an estimated $7.4 billion annually.

Ziska said his latest study is aimed at determining how six plants identified in federal surveys as those that cause the most crop damage will respond to the same climatic changes.

Ziska has shown that under controlled laboratory conditions, the plants thrive under higher temperatures and increased carbon dioxide levels.

But he wants to grow two of the plants, Canada thistle and morning glory, which crowd out corn and soybeans, at the three monitoring stations to see how they do in nature.

Ziska said the study is intended to understand plant characteristics and search for ways to minimize the damage they cause.

Scientists say that since the late 19th century, the Earth's surface temperatures have risen by about 1 degree Fahrenheit and that greenhouse gases - needed to trap heat in the atmosphere - have increased drastically. One, carbon dioxide, has increased by 30 percent since 1900, a change generally believed to be caused by factory and car emissions.

Many scientists believe the increase in greenhouse gases is causing global warming, but some scientists dispute that.

Ziska remains convinced that increasing levels of carbon dioxide have implications for much of the Earth's plant and wildlife. If rising levels of carbon dioxide are causing certain weeds to thrive, he said, they also will affect other plants and animals, he said.

"The question is, what are the effects on the rest of the food chain, what about the insects that feed on those plants, what about the birds that feed on those insects?" he said. "The implications are staggering."

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