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Excess CO2 May Bring Abundance of Weeds

By Robert C. Cowen / December 12, 1995



SHOWING a visitor around a forested research site, botanist Boyd Strain warns that ''aggressive weeds'' could inherit the earth.

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We should heed his warning. The carbon dioxide (CO2) pollution that may warm the planet is also ''fertilizing the atmosphere'' to use the Duke University researcher's phrase. For plants, CO2 is the breath of life. It supplies the carbon they need for growth. But nobody knows how the plant world will respond to the abundance of CO2. It could lead to a feeding frenzy by species that people consider undesirable - that is, a burgeoning of ''weeds.''

Hence Dr. Strain's warning. He considers the often expressed view that CO2-enriched air will be generally beneficial for farming and forestry to be misplaced optimism, a prediction based on ignorance. And that ignorance is dangerous. The consequences of CO2 enrichment will be upon us by the mid-21st century. If we don't know what to expect, we won't know what precautions - if any - we should be taking before then.

The cure for that ignorance is specific research into an aspect of CO2 pollution that has received far less attention than has its potential for global warming. CO2enrichment would have a profound effect on plant life even if there were no substantial climate change. Conversely, the possible effects of global warming on plants can't be understood without taking account of CO2's fertilizing influence.

That can change the mix of species on unmanaged land and change the populations of soil organisms and above-ground animals as well. Therefore, the relevant research has to take account of the whole system of birds, bees, rodents, fungi, microbes, and other inhabitants, as well as plants. That's why Strain's research site near Duke's Durham, N.C., campus sports some unusual ''trees.''

Sixteen towers encircle an area 100 feet in diameter. Operating under computer control, they emit CO2 at times and in amounts needed to maintain a 21st-century atmosphere within the circle. A 17th tower bristling with meteorological instruments monitors wind and other weather conditions to give the controlling computer the data it needs to maintain efficient CO2 dispersal.

This is the prototype with which Strain and co-investigator George Hendrey of Brookhaven National Laboratory at Upton, Long Island, N.Y. - who designed the setup - have shown how to study CO2 enrichment in the field. The site is big enough for specialists to study the soil while others look at plants, insects, and other animals. It will take many years for such research to reveal the ecological effects of CO2 enrichment. That's what Dr. Hendrey and Strain's Duke colleague William Schlesinger plan to do, now that the research setup has proved itself. They will build six similar sites in the forest - all complete with 16 encircling towers and central meteorological platform. Three of the sites will actively enrich their air with CO2. The other three will not have this enrichment. They are the experimental ''controls'' that will be used for comparison with the enriched areas. The sites will be at least 300 feet apart to minimize interference among them.

Dr. Schlesinger says it will take at least a decade for this Free Air Carbon Dioxide Enrichment (FACE) experiment to show the often subtle long-term ecological changes CO2 enrichment will bring. He adds that ''we're probably going to want to go on beyond year 10.'' It's an exercise in patience spiced with a sense of urgency.

Meanwhile, Strain says that whatever the changes may be, he expects that agriculture will successfully adapt, because it is actively managed. It's the unmanaged or poorly managed lands where undesirable changes may take place. That's where he expects weed species - not timber trees or forests as we know them today - to thrive.

That means that even lands we want to preserve in what we consider their ''natural state'' may need more active management than we anticipate. We can wait and be overtaken by unexpected changes. Or we can mount more research programs like FACE and be forewarned.