What was done
Circular FACE plots (30 m diameter) receiving 350 and 560 ppm CO2 were established two years ago in a 13-year-old loblolly pine plantation in North Carolina, USA, to determine the effects of elevated CO2 on forest productivity.  After one year of treatment, the researchers reported an initial 12% CO2-induced growth enhancement, but suggested that this response could well decline to zero within the coming decade.  This paper describes the results of their study at the end of two full years of differential CO2 exposure.

What was learned
After two years of atmospheric CO2 enrichment, the growth rate of dominant canopy pine trees was about 26% greater than that of trees grown in ambient CO2.  In addition, elevated CO2 increased total ecosystem net primary productivity by about 25% relative to that of plots maintained at ambient CO2.

What it means
As the CO2 content of the air continues to increase, loblolly pine plantations will likely experience ever-increasing productivity that ultimately could function as a "biological brake" to slow the rise in atmospheric CO2 concentration.  The observed 25% increase in productivity, for example, could absorb half of the anthropogenic CO2 emissions of the next century, the researchers say, if extrapolated globally to all forests. We shall eagerly await the results of year three!