By Paul Recer
The Associated Press
W A S H I N G T O N— In a study measuring the effect of a major greenhouse gas, researchers have found that trees exposed to increased carbon dioxide grow 25 percent faster than those without the extra CO₂.
     Researchers enriched the CO₂ atmosphere in 100-foot-wide plots of pine trees near Duke University in North Carolina to determine how the plants would respond to an increase in the atmospheric gas. 
     For at least the first two years of the experiment, the trees have thrived and grown more vigorously than did nearby trees without the added CO₂, said Evan H. DeLucia, the first author of study appearing in the May 14 edition of the journal Science.
     But neither DeLucia of the University of Illinois at Urbana nor William Schlesinger of Duke, principal investigators in the study, expect the enhanced growth of the trees to continue in later years. 
     “This probably will abate with time,” said DeLucia. He said that earlier studies of trees naturally exposed to high CO₂ levels show that a growth spurt from the added gas goes away after a few years. 

Carbon Dioxide In, Oxygen Out
     Plants absorb CO₂ and give off oxygen. Much of the carbon from the CO₂ is incorporated into branches, roots and trunk of the plants. 
     CO₂ is returned to the atmosphere when the plant parts decay or are burned. Burning of fossil fuels, such as oil and coal, also add CO₂ to the atmosphere. Some scientists believe that increased fuel use will cause global CO₂ levels to increase by 35 percent to 50 percent by 2050. 
     Increased CO₂ may warm the whole Earth, some scientists believe, because the gas blocks heat from returning to space and traps it about the planet. The gas acts like the glass in a greenhouse, letting sunlight in, but preventing the escape of heat. This is known as the greenhouse effect. 
     DeLucia said the pine tree experiment was an attempt to determine how forests might react to the expected CO₂ increase. 
     In three test plots, pipes steadily pumped in CO₂, keeping the gas level among the trees at 560 parts per million. Atmosphere levels at nearby control plots of trees remained at about 360 ppm. 
     Trees in the test plots grew at a rate 16 percent faster in the first year and 25 percent faster in the second year when compared with pines that had only the normal atmospheric CO₂. 
     These results, said DeLucia, suggest that global forests might absorb about half of the forecast increase in CO₂. 
     “Trees alone are not going to solve this problem for us,” said DeLucia.