Carbon storage in mature forests

April 2020: Mature forests may have limited capacities to absorb extra carbon in the atmosphere due to restricting environmental growth conditions. The results could significantly impact forest carbon accounting methods and severely impact government strategies to achieve carbon neutrality targets.

Information

Many countries, governments, and international bodies are developing strategies to decarbonise the economy and achieve net zero targets. Key elements of these strategies are natural climate solutions such as trees storing carbon and forests acting as carbon sinks. However, new evidence suggests that mature forests have limited ability to absorb additional carbon as atmospheric CO₂ emissions increase. Growing trees absorb carbon and can use additional carbon in the atmosphere to grow faster which is known as CO₂ fertilisation. Mature trees have limited growth capacity due to environmental factors such as space, soil nutrients, and root density. When mature trees have reached their growth limit, the extra carbon is quickly cycled through the soil and released back into the atmosphere by the trees themselves or fungi and bacteria in the soil. Consequently, mature trees capture less carbon than growing trees but continue storing previously captured carbon and converting carbon into oxygen.

Implications and opportunities

A limited capacity for mature forests to absorb carbon could impact strategies for carbon neutrality. Many models projecting future climate change scenarios are based on the assumption that mature forests will continue to absorb carbon above their current levels. However, carbon sinks may be lower or absent for mature forests, significantly changing global forest carbon assessments and forest carbon accounting. Researchers are recommending embedding carbon capture capacities in forest management practices and focusing on building climate smart forests. Climate smart forests could include a diverse range of old and young trees as well as a focus on species that may be better adapted to future climate conditions.

Limitations

The study is an exploratory study analysing Eucalyptus trees in Australia. All results should be seen within the study’s geographic and methodological context and further research will be needed to investigate the results’ generalisability. 

Sources

Jiang, M., et. Al. (2020). The fate of carbon in a mature forest under carbon dioxide enrichment. Nature, 580 (7802), 227–231. doi:10.1038/s41586-020-2128-9

Torre, G., (2020). Climate change could be worse than models predict as trees cannot sequester more carbon, study claims. Retrieved from: https://www.telegraph.co.uk/news/2020/04/13/climate-change-could-worse-models-predict-trees-cannot-sequester/