CO2-INDUCED GROWTH ENHANCEMENTS OF COOCCURRING TREE SPECIES DECLINE AT DIFFERENT RATES

To elucidate how enriched CO2 atmospheres, soil fertility, and light a vailability interact to influence the long-term growth of tree seedlin gs, six co-occurring members of temperature forest communities includi ng ash (Fraxinus americana L.), gray birch (Betula populifolia), red m aple (Acer rubrum), yellow birch (Betula alleghaniensis), striped mapl e (Acer pensylvanicum), and red oak (Quercus rubra L.) were raised in a glasshouse for three years in a complete factorial design. After thr ee years of growth, plants growing in elevated CO2 atmospheres were ge nerally larger than those in ambient CO2 atmospheres, however, magnitu des of CO2-induced growth enhancements were contingent on the availabi lity of nitrogen and light, as well as species identity. For all speci es, magnitudes of CO2-induced growth enhancements after one year of gr owth were greater than after three years of growth, though species' gr owth enhancements over the three years declined at different rates. Th ese results suggest that CO2-induced enhancements in forest productivi ty may not be sustained for long periods of time. Additionally, specie s' differential growth responses to elevated CO2 may indirectly influe nce forest productivity via long-term species compositional changes in forests.