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STRIKING RESULTS FROM BROOKHAVEN ECOLOGY FACILITY
"This study puts forests on the carbon dioxide map," said lead author and Illinois plant biologist Evan DeLucia. While the potential for forests to absorb carbon dioxide emissions had been only speculative, "now we have some real data that allows for global extrapolation," he added. If forests worldwide were to grow 25 percent faster in 50 years than they do now, the results would suggest that plant life could serve as a "sink" for about half the expected carbon dioxide emissions from fossil fuel combustion. But DeLucia and William Schlesinger, a Duke botany professor and the article's other main author, caution that such a high sustained uptake is unlikely. Commented Brookhaven's George Hendrey, who co-chairs FACTS-1 with Schlesinger and founded the Free Air Carbon Enrichment program, "These results confirm the value of simulating tomorrow's atmosphere in natural ecosystems - and raise important questions for future research." The Duke-owned forest where the DOE-funded study is being conducted is dominated by 13-year-old loblolly pines, among the fastest growing tree species, at their peak growing age. Also, open-air studies at Italian hot springs and another Duke plot suggest that carbon dioxide-induced growth spurts will decline within a few years. "The crux of the matter is that vegetation can respond to higher CO2 and act as a carbon sink," Schlesinger said. "The 25 percent growth increase is probably an upper limit for what the world's vegetation can do. Nevertheless, it's interestingly high." With technology pioneered by Brookhaven, three 100-foot diameter forest parcels, each ringed by 16 towers, are receiving atmospheric concentrations of carbon dioxide at 560 parts per million, as projected for the year 2050, compared to today's concentration of 360 parts per million. The extra CO2 is being delivered round-the-clock by pipes and valves on the towers. Computer controls ensure that the right valves open on the right towers to keep the distribution constant within all parts of each plot, regardless of wind direction and speed. The experiment is "fully replicated," meaning that trees in three locations are exposed to increased CO2. Three other identical tower-ringed forest plots that receive no extra CO2 are serving as controls whose response can be compared to the three treated sites. In 1997, the first full year of the replicated study, the overall growth rate of the dominant pine trees and underlying hardwoods, shrubs and vines increased 16 percent in the extra-CO2 plots when compared to control plots, the authors report in Science. In 1998, the increase swelled to 25 percent, an addition that to some degree reflected the inclusion of fine root growth not measured in 1997. The scientists are skeptical that high growth rates can be sustained, in part because of the Swiss and Italian studies. Those studies, comparing high-CO2 levels to control sites, found carbon dioxide's stimulatory effects decreased as trees age. An older tower ring site built to test the FACE concept has also logged reduced response to elevated CO2 beginning after the fourth of its six years of operation.
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