Recent research has found that mature forests can adapt to elevated CO2 levels by increasing their wood production, contradicting previous theories that they do not have this ability. This discovery, which is part of the ongoing BIFoR FACE experiment, highlights the importance of older forests for carbon sequestration and their role in combating climate change.
Old forests are crucial in the fight against climate change – they extract carbon dioxide (CO2) from the atmosphere and incorporates it into new wood.
In a groundbreaking study, researchers have demonstrated that older trees can significantly increase woody biomass production in response to elevated CO2 levels, challenging previous assumptions about mature forests. The findings from the BIFoR FACE experiment highlight the potential of mature forests to act as carbon sinks and contribute to climate change mitigation in the medium term, and underscore the need for sustainable forest management and policy support.
Researchers discovered that older trees responded to increased CO2 concentrations in the atmosphere2 by increasing the production of woody biomass – contrary to existing theories that mature forests are unable to respond to increased CO2 emissions.2 levels.
The experts concluded that exposure to elevated concentrations of the greenhouse gas (ambient air + 150 ppm CO2; an increase of about 40%) increased wood production by an average of 9.8% over a seven-year period. No corresponding increase in the production of material such as leaves or fine roots that release CO2 It has been proven that the substance enters the atmosphere relatively quickly.
Long-term carbon storage in forests
Their results were published today (12 August) in the journal Nature Climate Changesupport the role of mature forests as medium-term (decades-long) carbon stores and natural climate solutions – thanks to data from long-term CO2 measurements in the open air.2 Enrichment Experiment (FACE) at University of Birmingham‘s Institute of Forest Research (BIFoR) in central England.
Researchers at BIFoR conducted a FACE experiment in a 180-year-old deciduous forest dominated by 26-meter-tall pedunculate oaks – six plots with a diameter of 30 meters, three of which were exposed to elevated CO2 concentrations.2 The other three plots serve as controls.
Role of old forests in carbon sequestration
Lead author Professor Richard Norby of the University of Birmingham commented: “Our results challenge the idea that older, mature forests cannot respond to rising CO2 levels in the atmosphere. How they respond probably depends on the supply of nutrients from the soil.”
“The evidence presented by BIFoR FACE of a significant increase in woody biomass production underpins the role of mature, long-standing forests as a natural climate solution in the coming decades as society seeks to reduce its dependence on carbon.”
Future impacts on forest management
FACE experiments simulate future atmospheric composition and provide valuable data on the interaction between forests, atmosphere and climate. Previous experiments showed that forest productivity can increase under elevated CO2 levels.2 However, the studies were conducted in young tree plantations – which raises the question of whether older trees would respond in the same way.
Co-author and BIFoR Director Professor Rob MacKenzie of the University of Birmingham commented: “We believe these results, roughly halfway through our fifteen-year experiment at BIFoR FACE, will prove invaluable to policy makers around the world as they grapple with the complexities of climate change.
“FACE experiments like ours provide the basis for predictions of future atmospheric CO2 concentrations and thus significantly improve confidence in political decisions. But even if increased tree growth leads to an increase in carbon storage in forests in the medium term, this is by no means a reason to delay the reduction in fossil fuel consumption.”
The BIFoR FACE experiment began in 2017 by altering the atmosphere around the forest and measuring the effects of increased CO2 for wood production by converting measured tree diameters into wood mass using laser scanning.
Broader context of carbon storage in forests
The scientists calculated the total growth of the forest (the so-called net primary productivity, NPP) by combining the wood production of oaks and undergrowth trees with the production of leaves, fine roots, flowers and seeds, and even the amount of biologically active compounds released by the roots.
The researchers found that NPP was 9.7% and 11.5% higher with increased CO2 than under ambient conditions in 2021 and 2022 – an increase of about 1.7 tonnes of dry matter per hectare per year. Most of this increase was due to wood production, and there were no changes in fine root or leaf mass production.
To put this additional carbon storage in the forest into context: it corresponds to 1% of the CO2 emitted by a single commercial passenger plane on a one-way flight from London to New York. The total amount of carbon absorbed per hectare per year by a long-standing forest is ten times that. These values give an indication of the level of forest protection and management required to offset even significant fossil fuel emissions.
The BIFoR FACE experiment will continue into the 2030s to analyse long-term responses and interactions between forest carbon, other plant nutrients and the forest food web.
Reference: “Enhanced woody biomass production in a mature temperate forest under elevated CO2” by Richard J. Norby, Neil J. Loader, Carolina Mayoral, Sami Ullah, Giulio Curioni, Andy R. Smith, Michaela K. Reay, Klaske van Wijngaarden, Muhammad Shoaib Amjad, Deanne Brettle, Martha E. Crockatt, Gael Denny, Robert T. Grzesik, R. Liz Hamilton, Kris M. Hart, Iain P. Hartley, Alan G. Jones, Angeliki Kourmouli, Joshua R. Larsen, Zongbo Shi, Rick M. Thomas and A. Robert MacKenzie, 13 August 2024, Nature Climate Change.
DOI: 10.1038/s41558-024-02090-3
