Extensive areas occupied by Pinus nigra forests in Spain have burned in recent years. Recovery of these forests depends upon reforestation. In this study, we analyze the combined effects of different treatments of water restriction and air enrichment with CO2 in the nursery as a means to increase hardening and vigor of P. nigra seedlings of various ages (recently germinated, 1- and 2-year-old) and their post-transplant performance in a burned area. In all cases, 2-year-old seedlings showed the highest specific leaf weight and low cuticular transpiration rates. CO2 enrichment increased total biomass, leaf biomass and leaf area of seedlings while water restriction decreased leaf area, leaf biomass, and stem biomass, without any significant interaction between both experimental factors. Younger (recently germinated and 1-year-old) seedlings showed a larger relative response to the experimental factors than 2-year-old seedlings. After transplanting, the previous CO2 and water treatments did not affect seedling survival, but 2-year-old seedlings showed the lowest mortality rates.