What was done
The author reviewed 15 previously published studies of CO2-induced growth responses of trees with differing shade-tolerance in order to determine if knowledge of shade-tolerance can be used as a tool to predict tree growth responses to atmospheric CO2 enrichment.

What was learned
Elevated CO2 caused greater relative biomass increases in shade-tolerant species than in shade-intolerant species.  In fact, in more than half of the studies analyzed, shade-tolerant species experienced CO2-induced relative growth increases that were two to three times greater than those of less shade-tolerant species.

What it means
As the CO2 concentration of the atmosphere continues to rise, the tallest of forest trees that receive plenty of direct sunlight should grow better than they do today.  Some people have worried that their enhanced production of branches and leaves will enable them to out-compete smaller trees that grow in their shade.  The results of this study, however, suggest that the percentage CO2-induced growth increase should be much greater for these shade-tolerant species than it is for the trees that tower above them.  Consequently, it is likely that forest biodiversity will not be adversely affected by the ongoing rise in the air's CO2 content.