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.
Bibliographical noteFunding Information:
This research was principally supported by the U.S. Department of Energy's Office of Biological and Environmental Research, (Grant No. DE-FG02-95ER62125). Additional support was provided by the US Forest Service Northern Research Station and Northern Global Change Program, Michigan Technological University, the Praxair Foundation, the McIntire-Stennis Program, Natural Resources Canada-Canadian Forest Service and Academy of Finland (project 109933). The authors are grateful to Janet Pikkarainen and David B. Karnosky for their assistance in the manuscript editing and proof reading.
- Elevated tropospheric ozone and carbon dioxide
- Flower production
- Seed germination
- Seed quality
- Seedlings growth and survival