EMBARGOED FOR RELEASE UNTIL 2 P.M. CDT, THURSDAY, MAY 13
CONTACT: Jim Barlow, Life Sciences Editor (217) 333-5802; [email protected] or
Monte Basgall, Duke Senior Science Writer, (919) 681-8057; [email protected]
CHAMPAIGN, Ill. -- Experimental forest plots bathed in atmospheric carbon dioxide at levels expected by the year 2050 experienced a 25 percent growth increase during the first two years of a continuing project, University of Illinois and Duke University scientists report in the May 14 issue of the journal Science.
"This study puts forests on the CO2 map," said Evan DeLucia, a U. of I. plant biologist and the article's lead author. While the potential for forests to sop up increasing human-caused carbon dioxide emissions had been only speculative, "now we have some real data that allows for global extrapolation," he added in an interview.
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.
The forest, where the U.S. Department of Energy-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-inspired 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 in an interview. "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 the Brookhaven National Laboratory on Long Island, N.Y., 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 it is being repeated at three locations. Three other identical tower-ringed forest plots that receive no extra CO2 are serving as controls whose response can be compared to the three active sites.
Schlesinger is co-director of this Forest-Atmosphere Carbon Transfer and Storage (FACTS-1) experiment within part of the 7,700-acre university-owned Duke Forest research reserve, located several miles from the westernmost Duke campus. The other co-director is George Hendry, the Brookhaven researcher who devised the Free Air Carbon Dioxide Enrichment (FACE) delivery method.
In 1997, the first complete 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 the control plots, the authors reported in Science. In 1998, that increase swelled to 25 percent, an addition that to some degree reflected the inclusion of fine root growth that was not measured in 1997.
Both DeLucia and Schlesinger noted that those results occurred during two growing seasons that were affected by droughts. "The growth rates declined in the control plots as a result of the drought," while the high-CO2 plots "were able to make up for the drought," Schlesinger said. It may be that plants growing at higher carbon dioxide levels can better conserve water, he said. Separate studies have shown that plant stomata -- leaf pores that regulate water release -- do not open as widely in an environment of elevated CO2.
DeLucia, one of a number of scientists at work at the FACTS-1 site, is studying the "carbon budget" of the experimental plots.
DeLucia is measuring how much of the plants' carbon income is invested in new leaves, roots and stems, and how much is lost back into the atmosphere through respiration.
At the August 1998 Ecological Society of America meeting in Baltimore, Shawna Naidu, a postdoctoral researcher in DeLucia's lab, reported the 1997 growth rate in the high-CO2 plots at 12 percent in the first year. That number has been upped to 16 percent.
DeLucia and Schlesinger are skeptical that high growth rates can be sustained, in part because of Swiss and Italian studies of tree rings near hot springs near Pisa and Siena, Italy, that naturally emit carbon dioxide and other gases. The studies, comparing high-CO2 levels to control sites, found carbon dioxide's stimulatory effects decreased as trees age.
An older tower ring at the FACTS-1 site built to test the FACE concept also has logged reduced growth response to elevated CO2 beginning after the fourth of its six years of operation, Schlesinger said. But that plot only receives extra carbon dioxide during the daytime and is marred by "a lot of disturbance around the edge," he noted.
"In the few studies that have looked at how trees, such as those growing next to natural springs of CO2, respond over long periods of time, growth response is strong at first, then decays," DeLucia said. "Other models also predict this response. The mechanisms for this slowing of the growth response are not entirely clear; one reason is that trees may acclimate by slowing their photosynthesis rates."
Whether the increases end up being short term or longer term, the growth recorded during the first two years of the FACTS-1 study highlight the environmental downside of suburban sprawl that is invading woodlands in the South and elsewhere, Schlesinger said.
"To the extent that we convert any of these fast growing forested lands to parking lots and shopping centers, that carbon sink is totally gone," he added. "Not only is the sink gone, but the carbon that used to be in the trees has probably been returned to the atmosphere by burning the trees or using the wood products in things like paper towels and cardboard boxes that later decompose or are burned."
-jb-
END
ADVANCE FOR RELEASE AT 2 P.M. CDT, THURSDAY, MAY 13
RSS