A recent study highlights the vital role that mature forests play in combating climate change by absorbing carbon dioxide (CO2) from the air and storing it in the form of new wood.
The study indicated that when exposed to higher concentrations of the greenhouse gas (ambient atmosphere plus 150 parts per million CO2; roughly a 40% rise), wood production increased by an average of 9.8% over a seven-year timeframe. Interestingly, there was no similar rise in the production of leaves or fine roots, which typically release CO2 back into the atmosphere quickly.
Published today (12 Aug) in Nature Climate Change, these findings underscore the importance of mature forests as medium-term carbon storage solutions and natural remedies for climate change, supported by data from the long-running free-air CO2 enrichment (FACE) experiment conducted by the University of Birmingham’s Institute of Forest Research (BIFoR) in central England.
The researchers at BIFoR set up a FACE experiment in a 180-year-old deciduous forest primarily consisting of 26-meter-tall English (or ‘pedunculate’) oak trees. They created six plots with a diameter of 30 meters, three of which were exposed to elevated CO2 levels while the other three served as controls.
Professor Richard Norby, the lead author from the University of Birmingham, noted, “Our discoveries dismiss the idea that older, mature forests cannot respond to rising atmospheric CO2 levels, although their response may be influenced by nutrient availability in the soil.”
“The significant increase in woody biomass production observed in the BIFoR FACE experiment supports the notion of established forests as natural solutions for climate change in the years to come, especially as society seeks to decrease carbon reliance.”
FACE experiments simulate future atmospheric conditions, yielding important data on the interplay between forests, atmospheres, and climate. Previous studies indicated that tree productivity can rise in response to elevated CO2, but these were mainly conducted on young plantations, raising concerns about whether older trees would show similar results.
Co-author and BIFoR Director Professor Rob MacKenzie from the University of Birmingham stated, “We anticipate that these findings, coming around the midpoint of our fifteen-year BIFoR FACE experiment, will be crucial for global policymakers as they confront the intricacies of climate change.”
“Experiments like ours lay the groundwork for future predictions regarding atmospheric CO2 levels, greatly enhancing the confidence in policy-making. However, despite the increase in tree growth potentially leading to greater medium-term carbon storage in forests, it should not be interpreted as a reason to postpone fossil fuel reduction efforts.”
The BIFoR FACE experiment commenced altering the forest’s atmosphere in 2017 and has been assessing the impact of heightened CO2 on wood production by employing laser scanning techniques to convert measured tree diameters into wood mass.
Scientists determined the overall growth of the forest, termed net primary productivity (NPP), by combining the wood production of the oaks and understory plants with that of leaves, fine roots, flowers, seeds, and the biologically active compounds released by the roots.
The research revealed that NPP was 9.7% and 11.5% higher under elevated CO2 conditions compared to normal conditions in 2021 and 2022, respectively—an approximate increase of 1.7 tons of dry matter per hectare per year. Most of this boost was attributed to wood production, with no changes in the mass production of fine roots or leaves.
To contextualize the additional carbon storage provided by the forest, this increase amounts to about 1% of the CO2 emitted by a single commercial flight from London to New York, one-way. In total, the carbon absorbed by the mature forest per hectare annually is ten times greater. These figures illustrate the extent of forest protection and management necessary to offset even essential fossil fuel emissions.
The BIFoR FACE experiment will continue into the 2030s to study long-term reactions and the interactions among forest carbon, other plant nutrients, and the forest food web.
