Mitigating Global Warming

Trees May Not Play as Big a Role as Scientists Hoped p.3

"Parts of the trees that fall to the ground and die each year might very well store the carbon in the soil," he continued. The alternative, he said, would be "decomposition"of the carbon compounds by microbes.

"What we saw was that the decomposers do an awfully good job of working their way through all this dead material, breaking it down, and returning the carbon dioxide to the atmosphere," Schlesinger said.

Looking like a science fiction spaceport from the air, with its seven rings pockmarking the green landscape of Duke Forest like arboreal crop circles, FACE is indeed futuristic, though science fact rather than fiction.

It traces its own roots to pioneering work by Boyd Strain, a now-retired Duke botany professor and former director of Duke's Phytotron, a high-tech greenhouse. It was Strain who did many of the initial studies on how extra carbon dioxide affects plants growing in indoor and outdoor chambers much less elaborate than FACE.

In his quest for more real-worldly experimental conditions, Strain turned to George Hendrey, of Brookhaven National Laboratory, who has built several open-air FACE facilities around the world.

The idea was to have an outdoor laboratory "without the experimental artifacts that a 'bag' or a greenhouse would create," said Schlesinger, who took over from Strain.

The first prototype tower ring, built in 1993, tested whether computer-controlled valves could deliver reliable concentrations of CO₂ to the Duke Forest tracts regardless of wind and weather conditions.

Oren also used the prototype to study elevated carbon dioxide's effects on transpiration, the loss of water vapor from leaves. "It was never our intention to study tree growth at all there," he said. But to evaluate transpiration they had to measure tree diameters. "And we suddenly saw a very large increase after the CO₂ was turned on," he recalled.

Most of the research at FACE is done in six other tower rings completed in 1996, three of which emit carbon dioxide. Three other tower rings are used as "controls" where all conditions are the same as in the first three except for elevated CO₂.

Since the prototype has no matched control plot, Oren's group had to use a statistical technique to compare their initial growth results to those DeLucia's team had measured in the other rings with matched controls.

A new Department of Energy grant of slightly more than $1 million a year will keep the FACE site operating through July 2004.

"Usually when you send in a big grant proposal the funding agency reviews it and sends you a list of criticisms," Schlesinger said. "Then you have to submit an addendum where you answer the criticisms and say how you're going to do it better. But this was funded in full without having to do an addendum. "So we regard this as a real seal of approval."

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