What was done
The author conducted a literature review of 24 studies that reported 74 woody-plant growth responses to elevated CO2.  Data were analyzed and grouped according to whether the studied species were deemed to be shade-tolerant or shade-intolerant.  Evaluations were based on growth response to a doubling (700 ppm vs. 350 ppm) of the atmospheric CO2 concentration.

What was learned
Elevated CO2 increased the relative growth response of shade-tolerant woody species by an average of 51%, while it increased the relative growth response of shade-intolerant species by approximately 18%.  Thus, although typically exhibiting slower growth rates, shade-tolerant species exhibited greater CO2-induced increases in biomass than more rapidly growing shade-intolerant species.

What it means
As the CO2 concentration of the air increases, shade-tolerant woody plants will likely increase their biomass by close to three-fold more, on a percentage basis, than shade-intolerant species.  This advantage should provide for greater seedling survival and establishment of shade-tolerant plants in the types of low-light environments that prevail on forests floors beneath tall and dense forest canopies.