The Science

A synthesis of long-term, U.S. Department of Energy (DOE)–supported experiments shows that in young temperate forests tree biomass growth increased by 30% in response to a decade of carbon dioxide (CO₂) enrichment. This response was predictable with knowledge of the plant production response to CO₂ and the relationship of wood production to whole-plant production under ambient CO₂ conditions.

The Impact

CO₂ fertilization is the stimulation of gains in plant biomass by increased atmospheric CO₂, which creates a feedback on the rate of increase in atmospheric CO₂. The complexity combined with the global and decadal scales of this process means that estimates of the size of the feedback remain uncertain. By synthesizing the longest running experiments in forest or woody ecosystems, this study develops understanding of the processes that determine CO₂ fertilization at longer timescales and ecosystem spatial scales.

Summary

Stimulation of photosynthesis by increasing atmospheric CO₂ can increase plant production, but at longer timescales it may not necessarily increase plant biomass because all the additional production could be in short-lived tissues such as leaves and fine roots. An international team of scientists, led by Oak Ridge National Laboratory, analyzed the four decade–long CO₂ enrichment experiments in forests that measured total plant production and biomass (including below ground). Using statistical mixed-models they showed that CO₂ enrichment increased biomass increment by 1.05 ± 0.26 kg of carbon per m² (kg C m^–2) over a full decade. This response was predictable with knowledge of the production response to CO₂ (0.16 ± 0.03 kg C m^–2 y^–1) and the biomass retention rate (slope of the relationship between biomass increment and cumulative production; 0.55 ± 0.17), which was independent of CO₂. An ensemble of terrestrial ecosystem models failed to predict both terms correctly, but with different reasons among sites. These results demonstrate that a decade of CO₂ enrichment stimulates live-biomass increment in temperate, early-succession, forest ecosystems. CO₂ independence of the biomass retention rate highlights the value of understanding ambient conditions for interpreting CO₂ responses.

Principal Investigator

Anthony Walker
Oak Ridge National Laboratory
walkerap@ornl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

Support by the Free Air CO₂ Enrichment Model Data Synthesis (FACE-MDS) of the Office of Biological and Environmental Research within the U.S. Department of Energy (DOE) Office of Science,

References