Effects of decadal exposure to interacting elevated CO2 and/or O3 on paper birch (Betula papyrifera) reproduction.

Abstract: We studied the effects of long-term exposure (nine years) of birch (Betula papyrifera) trees to elevated CO₂ and/or O₃ on reproduction and seedling development at the Aspen FACE (Free-Air Carbon Dioxide Enrichment) site in Rhinelander, WI. We found that elevated CO₂ increased both the number of trees that flowered and the quantity of flowers (260% increase in male flower production), increased seed weight, germination rate, and seedling vigor. Elevated O₃ also increased flowering but decreased seed weight and germination rate. In the combination treatment (elevated CO₂ +O₃) seed weight is decreased (20% reduction) while germination rate was unaffected. The evidence from this study indicates that elevated CO₂ may have a largely positive impact on forest tree reproduction and regeneration while elevated O₃ will likely have a negative impact. [Copyright &y& Elsevier]