We review the results of several experiments on growth of potted and free rooted Castanea sativa and Fagus sylvatica in soils of differing nutrient contents under CO2 enrichment with respect to the CO2 responses of gas exchange, biomass increments, tissue chemistry, allocation and canopy development. The stimulation of leaf photosynthesis and plant growth by elevated CO2 is shown to be modulated by the balance of resource availability. High soil resources allow for high increases in photosynthesis and growth. Fagus shows a higher growth response to elevated CO2 than Castanea. The feedbacks between stimulation of leaf photosynthesis by elevated CO2 and LAI expansion are important factors to be taken into account when it comes to extrapolation of experimental results on young trees to mature forests.