What was done
In a study that extends and builds upon similar work they conducted five years earlier (LaDeau and Clark, 2001), the two biologists determined the reproductive responses (cone and seed production) of loblolly pine (Pinus taeda L.) trees to atmospheric CO2 enrichment at the Duke Forest FACE site in the Piedmont region of North Carolina, where in August of 1996 three 30-m-diameter FACE rings began to enrich the air around the 13-year-old trees they encircled to 200 ppm above the atmosphere's normal CO2 concentration, while three other FACE rings served as control plots at the air's ambient CO2 concentration.

What was learned
LaDeau and Clark determined that "carbon dioxide enrichment affected mean cone production both through early maturation and increased fecundity," so that "trees in the elevated CO2 plots produced twice as many cones between 1998 and 2004 as trees in the ambient plots." They also report finding that trees grown in elevated CO2 "made the transition to reproductive maturation at smaller [trunk] diameters," and that they "not only reached reproductive maturation at smaller diameters, but also at younger ages." By 2004, for example, they say that "roughly 50% of ambient trees and 75% of fumigated trees [had] produced cones." In addition, they observed that "22% of the trees in high CO2 produced between 40 and 100 cones during the study, compared with only 9% of ambient trees."

What it means
"In this 8-year study," in the words of the researchers who conducted both the initial and most recent work on the trees' reproductive capacities, "we find that previous short-term responses indeed persist," in contradiction of the opinions of biological pessimists who attempt to downplay the immense biological benefits of atmospheric CO2 enrichment. Furthermore, noting that "P. taeda trees that produce large seed crops early in their life span tend to continue to be prolific producers (Schutlz, 1997)," they conclude that this fact, together with their findings, suggests that "individual responses seen in this young forest may be sustained over their life span."

References
LaDeau, S.L. and Clark, J.S. 2001. Rising CO2 levels and the fecundity of forest trees. Science 292: 95-98.

Schutlz, R.P. 1997. Loblolly Pine - The Ecology and Culture of Loblolly Pine (Pinus taeda L.). USDA Forest Service Agricultural Handbook 713. USDA Forest Service, Washington, DC, USA.