The Unexpected Heroes in Methane Removal

Microbes living in tree bark are quietly combating climate change.

I have always loved trees. And yes, anyone who knows me describes me as a ‘tree-hugger’ — a moniker I take much pride in.

Something about them mesmerizes me. They are the truest representation of stoicism and resilience, combating the elements while quietly providing us with innumerable ecosystem services.

Growing up, my hometown had hundreds of plane trees with their characteristic peeling bark. I vividly remember peeling their bark off, something that kept me entertained for hours. I would scrutinize the little pieces and the scar they left behind and wonder “why do trees have bark?”

I soon learned that bark provides many benefits for trees, most related to protection against weather elements and parasites. However, this week, I learned something about bark that had never occurred to me: its role in combating climate change.

Trees have long been celebrated for their role in absorbing carbon dioxide (CO2) and providing oxygen, but recent research has uncovered a surprising new way they help combat climate change.

A study published in Nature reveals that trees also play a significant role in removing another greenhouse gas from the atmosphere: methane (CH4).

But how? Well, it all boils down to the microbes living in their bark. This discovery enhances our understanding of the global methane cycle and stresses the importance of forest conservation and reforestation efforts.

Methane is a potent greenhouse gas responsible for 20–30% of global warming since the Industrial Revolution and has 28 times the global warming potential of CO2 over 100 years.

Its atmospheric concentration has been rising rapidly, making it crucial to identify and quantify all sources and sinks of this gas. While soils have been known to act as methane sinks through the activity of methane-consuming bacteria, this new study shows that trees, particularly those in upland forests, also contribute significantly to methane removal.

https://www.forbes.com/sites/stevensavage/2024/04/25/methane-eating-microbesa-novel-solution-for-greenhouse-gas-mitigation/

To explore the role of trees in methane uptake, an international team of researchers led by Dr. Vincent Gauci from the University of Birmingham conducted extensive measurements across various forest ecosystems.

They focused on upland tropical, temperate, and boreal forests, with study sites in very different ecosystems, including the Amazon and Panama, Wytham Woods in the UK, and boreal forests in Sweden. Quite a dream study design.

Using gas exchange chambers and laser-based analyzers (I know, it sounds like a sci-fi plot), the team measured methane fluxes at different heights on tree stems. They also extracted wood cores to assess microbial methane consumption and used terrestrial laser scanning (TLS) to quantify the global tree woody surface area.

The findings were surprising. The researchers discovered that tree bark, especially at heights above 2 meters from the forest floor, acts as a significant sink for atmospheric methane.

Microbial activity in the bark consumes methane, a process known as ‘methanotrophy.’ This microbial action is so effective that trees’ methane uptake even rivals that of soils, which had been considered the primary terrestrial methane sink. It’s an example of why we should never make assumptions about the natural world.

Methane absorption was particularly strong in tropical forests, where warm and moist conditions favor microbial activity. Temperate and boreal forests also showed methane uptake, albeit at lower rates (see the different scales of the figures above).

The study estimates that globally, trees contribute between 24.6 and 49.9 teragrams (Tg) of methane uptake annually. This newly identified sink makes trees about 10% more beneficial for climate mitigation than previously thought. In other words, we have 10% more reasons to preserve forests.

Yadvinder Malhi, a co-author from the University of Oxford, highlighted the significance of these findings, saying, “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.”

This research has important implications for understanding the global methane budget (methane in the atmosphere vs. methane out of the atmosphere). Methane emissions have been rising faster than ever since records began in 1983, and the global methane budget is currently unbalanced, with sources exceeding sinks.

This study helps to close the gap in our understanding of methane sources and sinks by identifying trees as a major methane sink.

The findings also reinforce the climate benefits of forest protection and reforestation. We now know that forests sequester carbon dioxide through photosynthesis and remove methane from the atmosphere, providing a dual climate benefit. Professor Vincent Gauci noted, “Our results suggest that planting more trees and reducing deforestation surely must be important parts of any approach towards reducing methane emissions.”

Additionally, the discovery opens up new routes (or roots) for research. For example, the team plans to investigate whether deforestation has contributed to increased atmospheric methane levels and further investigate the mechanisms used by the microbes to uptake methane. They aim to explore if this natural methane removal process can be enhanced, potentially offering a new strategy for mitigating methane emissions.

The Nature study sheds light on a previously unrecognized climate service trees provide. By absorbing methane through their bark, trees contribute more to climate mitigation than carbon dioxide sequestration.

This is especially relevant considering that some forest ecosystems have already changed their carbon cycles and can no longer be considered carbon sinks. Current events, including wildland fires, insect infestations and pests, and logging, are slowly turning them into carbon sources for carbon dioxide. This has been observed in different ecosystems, including the Boreal forests of Canada and the Brazilian Amazon.

However, this finding offers some hope, indicating that forests are simultaneously sequestering other harmful greenhouse gases beyond carbon dioxide. This further reinforces the importance of conserving existing forests and expanding forested areas through reforestation and afforestation initiatives.

Further, the policy implications are clear. Efforts to reduce greenhouse gas emissions should focus on cutting CO2 and consider the role of methane and the various natural processes that can help mitigate its impact.

For instance, the Global Methane Pledge, which aims to cut methane emissions by 30% by the end of the decade, could benefit from incorporating strategies that enhance natural methane sinks, such as protecting and planting more trees.

Trees are proving to be even more valuable allies in the fight against climate change than we previously realized. Thanks to the hidden work of microbes in their bark, we know know that trees can remove methane from the atmosphere at a significant rate, adding another layer to why forest conservation and reforestation are critical for a sustainable future.