What was done
Circular FACE plots (30 m diameter) receiving 350 and 560 ppm CO2 were established in a 13-year-old loblolly pine plantation in North Carolina, USA, to determine the effects of elevated CO2 on the productivity of canopy and understorey species in the ecosystem.  This paper describes the results after one full year of differential CO2 exposure.  It is interesting to note that soils in the study region are characteristically low in available nitrogen and phosphorus.  Hence, any CO2-induced growth responses of trees in the FACE plots occur in the face of these nutrient limitations.

What was learned
After one year of atmospheric CO2 enrichment, the growth rate of dominant canopy pine trees was about 24% greater than that of trees grown in ambient CO2, in spite of the likelihood of soil nutrient limitations and a severe summer drought (rainfall in August 1997 was about 90% below the 50-year average).  In addition, atmospheric CO2 enrichment increased the biomass of canopy pines by about 14%.  However, elevated CO2 had no significant impact on the growth rate or biomass of the four most abundant understorey species (loblolly pine, sweetgum, winged elm and red maple) located within the study plots.

What it means
As the CO2 content of the air continues to increase, loblolly pine plantations will likely experience increases in growth rate and biomass production even on nutrient-poor soils and during times of drought, as indicated by the results of this study, which incidentally, is the first large-scale CO2 enrichment experiment conducted on an intact forest system with the full complement of species interactions and environmental stresses.