To elucidate how atmospheric CO 2 enrichment, enhanced nutrient supply and soil quality interact to affect regrowth of temperate forests, young Fagus sylvatica and Picea abies trees were grown together in large model ecosystems. Identical communities were established on a nutrient-poor acidic and on a more fertile calcareous soil and tree growth, leaf area index, fine root density and soil respiration monitored over four complete growing seasons. Biomass responses to CO 2 enrichment and enhanced N supply at the end of the experiment reflected compound interest effects of growth stimulation during the first two to three seasons rather than persistent stimulation over the whole duration of the experiment. Whereas biomass of Picea was enhanced in elevated CO 2 on both soils, Fagus responded negatively to CO 2 on acidic but positively on calcareous soil. Biomass of both species profited from enhanced N supply on the poor acidic soil only. Leaf area index on both soils was greater in high N supply as a consequence of a stimulation early in the experiment, but was unaffected by CO 2 enrichment. Fine root density on acidic soil was increased in high N supply, but this did not stimulate soil respiration rate. In contrast, elevated CO 2 stimulated both fine root density and soil CO 2 efflux on calcareous soil, especially towards the end of the experiment. Our experiment suggests that future species dominance in beech-spruce forests is likely to change in response to CO 2 enrichment, but this response is subject to complex interactions with environmental factors other than CO 2 , particularly soil type.