What was done
Based on tree-ring width and density data, the authors developed century-long chronologies of net primary productivity (NPP) for 21 Pinus halepensis forest stands in the southeast of France.  After determining what they could learn about the strength of the aerial fertilization effect of atmospheric CO2 enrichment from this exercise, they used the response functions they developed to calculate the effects of this phenomenon, as well as the effects of global warming, on the future of these particular French forests.

What was learned
The results of the present study were low compared to those of other such studies of French forests, which have shown productivity increases on the order of 100% over the 20th century.  Nevertheless, the authors' results still portended significant growth enhancements throughout the current century.  Under a doubled-CO2 scenario of enhanced greenhouse and aerial fertilization effects, for example, they calculated NPP increases for 14 of the 21 stands studied, obtaining enhancements that ranged from 8 to 55%.

What it means
The results of this study suggest that the historical increase in the air's CO2 content has benefited the forests of France, and that future CO2 increases will benefit them even more.  Indeed, the authors say "the physiological effect of CO2 could be more important than the effects of climatic change on forest productivity."  And they are right!