A surprising new climate benefit is found in tree bark
They’re well known for their carbon storing properties but now scientists have discovered that trees have an additional climate benefit, in their bark.
Professor Yadvinder Malhi, Director of the Leverhulme Centre for Nature Recovery, is among an international team of colleagues who have found tree bark surfaces play an important role in removing methane gas from the atmosphere.
Writing in the journal Nature they say microbes hidden within tree bark can absorb methane – a powerful greenhouse gas – from the atmosphere. Methane is responsible for around 30 per cent of global warming since pre-industrial times and emissions are currently rising faster than at any point since records began in the 1980s.
The team of researchers has shown for the first time that microbes living in bark or in the wood itself are removing atmospheric methane on a scale equal to or above that of soil. They calculate that this newly discovered process makes trees 10 per cent more beneficial for climate overall than previously thought.
Former Environmental Change Institute (ECI) Postdoc Researcher, Dr Allie Shenkin and Prof Malhi used detailed 3D laser scans of trees to estimate the total surface area of bark, both in particular woods and at the planetary scale. Prof Malhi said the tree shape analysis shows that if all the bark of all the trees of the world were laid flat, the area would be equal to the Earth’s land surface.
Prof Malhi said: “Tree woody surfaces add a third dimension to the way life on Earth interacts with the atmosphere, and this third dimension is teeming with life, and with surprises.”
In the study, the researchers investigated upland tropical, temperate and boreal forest trees. They took measurements spanning tropical forests in the Amazon and Panama; temperate broadleaf trees in Wytham Woods, in Oxfordshire, and boreal coniferous forest in Sweden.
Prof Malhi added: “Once again research carried out at the University of Oxford’s Wytham Woods has shown what an important area of study they are and it’s exciting to see they can still reveal surprises of planetary importance.”
Wytham Woods has been owned and maintained by the University of Oxford since 1942. The woods are often quoted as being one of the most researched pieces of woodland in the world, and their 1000 acres are designated as a Site of Special Scientific Interest.
The site is exceptionally rich in flora and fauna, with over 500 species of plants, a wealth of woodland habitats, and 800 species of butterflies and moths.
Prof Myles Allen, Climate programme lead at the ECI, and Head of Atmospheric, Oceanic and Planetary Physics in the Department of Physic provided valuable insights into how best to calculate the climate change implications of this absorption of methane, enabling the additional climate benefit of protecting or restoring trees to be calculated.
Although most methane is removed by processes in the atmosphere, soils are full of microbes that absorb the gas and break it down for use as energy. Soil had been thought of as the only terrestrial sink for methane, but the researchers now show that trees may be as important, perhaps more so.
Lead researcher on the study, Professor Vincent Gauci of the University of Birmingham, said: “The main ways in which we consider the contribution of trees to the environment is through absorbing carbon dioxide through photosynthesis, and storing it as carbon. These results, however, show a remarkable new way in which trees provide a vital climate service.
“The Global Methane Pledge, launched in 2021 at the COP26 climate change summit aims to cut methane emissions by 30 per cent by the end of the decade. Our results suggest that planting more trees, and reducing deforestation surely have to be important parts of any approach towards this goal.”
The methane absorption was strongest in the tropical forests, probably because microbes thrive in the warm wet conditions found there. On average the newly discovered methane absorption adds around 10% to the climate benefit that temperate and tropical trees provide.
By studying methane exchange between the atmosphere and the tree bark at multiple heights, they were able to show that while at soil level the trees were likely to emit a small amount of methane, from a couple of metres up the direction of exchange switches and methane from the atmosphere is consumed.
In addition, the team used laser scanning methods to quantify the overall global forest tree bark surface area, with preliminary calculations indicating that the total global contribution of trees is between 24.6-49.9 Tg (millions of tonnes) of methane. This fills a big gap in understanding the global sources and sinks of methane.
This new discovery opens up whole new directions of research. It is not known which bark types or trees species are better hosts for these methane-eating microbes, how quickly new trees build a methane-absorbing function, or whether the as yet unmeasured branches of trees are ever stronger methane absorbers.
Read the full paper in Nature: Global atmospheric methane uptake by upland tree woody surfaces
