What was done
For a full eleven years, the authors enriched the air with an extra 350 ppm of CO2 within half of a set of sixteen open-top chambers that enclosed portions of a fire-regenerated Florida (USA) scrub-oak ecosystem, which was comprised of a mix of three oak species (Quercus myrtifolia, Q. geminata and Q. chapmanii) that accounted for about 90% of the total aboveground ecosystem biomass, plus several other plant species that accounted for the remaining 10% of the ecosystem biomass.

What was learned
Seiler et al. report that the relative growth-enhancing effect of the elevated atmospheric CO2 concentration on community biomass increased steeply during the first three years of their study, reaching 67.3% in 1999, and that this overall community biomass stimulation remained stable for the duration of the experiment, such that at the time of final harvest, the overall CO2-induced biomass stimulation was 67.5%. Breaking this result down just a bit, their data also indicated that the species specific CO2-induced biomass stimulation at the end of their study was a huge 128% for Q. myrtifolia, a minor 6% for Q. geminata, and a whopping 217% for Q. chapmanii, although the latter species was only responsible for about 3% and 6% of the total aboveground biomass in the ambient and CO2-enriched chambers, respectively.

What it means
The ten researchers say the results of their long-term study show that "atmospheric CO2 concentration had a consistent stimulating effect on aboveground biomass production." This is a typical finding of studies of long-lived woody plants that have been maintained for periods of several years, as is demonstrated by the results of several of them that are described and archived under Long-Term Studies (Woody Plants) in our Subject Index.

Reference
Kimball, B.A., Idso, S.B., Johnson, S. and Rillig, M.C. 2007. Seventeen years of carbon dioxide enrichment of sour orange trees: final results. Global Change Biology 13: 2171-2183.