Anthony P. Walker
28 February 2019
Synthesis of four long-term, DOE supported, CO2 enrichment experiments show that young temperate forests increase carbon uptake at climate change–relevant timescales.
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.
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.
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.
BER Program Manager
Office of Biological and Environmental Research, SC-23.1
Anthony P. Walker
Oak Ridge National Laboratory
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,
Walker, A. P. et al. "Decadal biomass increment in early secondary succession woody ecosystems is increased by CO2 enrichment." Nature Communications 10, 454 (2019). [DOI:10.1038/s41467-019-08348-1].