Future Atmosphere Can Sustain Higher Tree Growth Rates

The Science

Plants use carbon dioxide in the air to make sugars to grow leaves, wood, and roots. Higher amounts of carbon dioxide in the air can stimulate this sugar production, but other factors also limit plant growth. Insufficient nitrogen in the soil can restrict any stimulation of plant growth by higher carbon dioxide. For 14 years, researchers increased carbon dioxide levels in the air of a loblolly pine plantation in North Carolina. They found despite evidence for nitrogen limitation in the forest, carbon dioxide stimulated growth over the whole time of the experiment.

The Impact

Increasing carbon dioxide in the air is causing climate change. However, carbon dioxide also stimulates plant growth, which removes carbon dioxide from the atmosphere and stores it in leaves, roots, wood, and soil. Removal and storage create a negative feedback loop on carbon dioxide increase in the air. This feedback is slowing the pace of climate change. Quantifying this feedback and understanding how long it will last help researchers predict how fossil fuel use translates into temperature increase. In turn, this understanding allows scientists and policy makers to design scenarios that meet international agreements limiting warming from climate change.

Summary

Scientists ran an experiment that elevated atmospheric carbon dioxide levels in a pine plantation with mixed-in hardwoods for more than 14 years. The forest was selected due to its moderate fertility and expectation of nitrogen limitation of the carbon dioxide effect. Carbon dioxide increased forest growth rates by almost 40%. Despite expectations that nitrogen would increasingly limit forest growth response, there was no evidence of decline, and 40% was maintained for the full duration of the experiment. Nitrogen was added to half of each plot in the final 6 years of the experiment, which increased growth by 10% at both carbon dioxide levels.

The carbon dioxide response in pine trees was a result of higher photosynthesis per leaf and higher amounts of leaves. Growth increased in pine trees’ leaves, stems, and roots. In broadleaf trees, the response was from higher photosynthesis per leaf, and additional growth was restricted to the root system. Forests with high carbon dioxide levels had more biomass at the experiment’s end due to higher growth, a higher proportion of wood growth, and reduced tree mortality.

Principal Investigator

Ram Oren
Duke University
[email protected]

Co-Principal Investigator

Anthony Walker
Oak Ridge National Laboratory
[email protected]

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

The Duke Free-Air Carbon Dioxide Enrichment (FACE) experiment and FACE Model-Data Synthesis project were funded by the Biological and Environmental Research program within the U.S. Department of Energy’s Office of Science.

Support for analysis was provided by the Atmosphere and Climate Competence Center Flagship–University of Helsinki, funded by the Academy of Finland (Grant 337549).

Related Links

• Duke FACE meterological data
• Duke FACE plant and soil response data

References