Researchers now have discovered that trees could be playing an enormous role in soaking up methane, a very potent greenhouse gas. According to a new study published in Nature, the finding overturns previous thinking and gives new significance to forests in the fight against climate change.
Traditionally, studies measured methane emissions from the bottom meter of the tree’s trunk. It is where methane emissions were originally discovered in trees. Now, in research conducted by experts from the University of Birmingham in collaboration with CREAF above this height, something was found quite unexpected. Measurements higher up the trunk showed that at about two meters and upwards the amount of methane absorbed by bacteria living in the bark was far greater than that emitted by trees into the atmosphere.
According to Josep Barba, a CREAF researcher, and co-author of the study, “forests on this planet could assimilate between 24.6 and 49.9 Tg of methane, a flux similar in magnitude to that which soils globally capture.” This study found that under warmer and more humid climates, like in forests—especially in tropical ecosystems—the highest rates of methane uptake occurred due to increased activity by microorganisms under these conditions.
The key players in this are bark-dwelling methanotrophs, which are bacteria powered by the gas methane. Essentially, these bacteria begin to utilize methane from the atmosphere when the concentration of this gas inside the wood gradually weakens two meters upward. “A tree acts like a chimney, drawing methane up from deep layers of the soil through its trunk and emitting the gas through its bark,” Barba explained. “So, the further up the trunk you go, the smaller the amount of methane remaining within gets.”
The research team conducted their study in a variety of forest ecosystems: the tropical forests of Panama and Brazil, the boreal forests of Sweden, and the temperate zones of England. Monitoring measuring chambers were attached to trunks, thus establishing real-time gas emission and absorption via bark, and samples of wood for the measurement of methane content and bacterial methane consumption. The results indicated that tropical forests capture the greatest amount of methane and are followed by the temperate and then the boreal.
This discovery added a new dimension, focussed on the role of forests in mitigating climate change. They not only capture carbon dioxide but also methane, hence making them more important against global warming. “The Global Methane Pledge, launched at the COP26 climate change summit in 2021, aims to cut methane emissions by at least 30% by 2030,” explained Vincent Gauci of the University of Birmingham, a co-author of the study. “Our findings suggest that tree planting and reduced deforestation should be two of the main planks of any strategy to achieve that goal.”
This was research involving a worldwide consortium of institutions such as the University of Birmingham, University of Lancaster, University of Oxford, The Open University, Northern Arizona University, Linköping University, Federal University of Rio de Janeiro, Smithsonian Tropical Research Institute, Ulm University, and CREAF, among others.
The new understanding of their potential for methane resorption might refocus strategies in reforestation. Though young forests cannot fulfill the purpose as effective carbon sinks due to low biomass, the possibility of methane capture is high because of the great bark surface area. “The age of trees doesn’t matter; provided it is plenty in number, there will be lots of exposed trunk surface and the potential for capturing methane from the atmosphere will be high,” said Barba.
In summary, this work underlines the complex role of forests in climate change mitigation: trees underline conservation and reforestation actions given their double effect in absorbing CO2 and CH4. The more we unravel the secrets of our natural world, the more evident it becomes that taking good care of our existing forests and expanding them is the only way to have some chance at survival in a sustainable future.