Trees have a well-earned reputation as climate heroes for their ability to suck up carbon dioxide and respire oxygen.
But until now, people have been overlooking tinier but far more numerous parts of the equation: the trillions of bacteria inhabiting tree bark.
Scientists in Australia spent five years peering into the microscopic world of bark, emerging with a description of a place teeming with life, much of it consuming and “exhaling” gases important for the climate. They dubbed it the “barkosphere.”
The numbers alone are staggering. A single square meter of this woody substance can be home to 6 trillion microbes, the scientists reported last week in Science. And there’s enough bark in the world to cover nearly every square meter of land on Earth.
Until recently, trees’ outer skin had been largely ignored. The microbes’ “existence and roles have been overlooked for many decades,” said Pok Man “Bob” Leung, a scientist at Monash University in Australia, who was involved in the new work.
It’s not just the sheer numbers that matter, it’s what they do. “Remarkably, most of these microbes are tree-adapted specialists that feed on climate-active gases,” Leung said.
The researchers discovered this by sampling bark from eight species of Australian trees in a variety of ecosystems, from swamps to upland forests. They then scanned the genetic material collected with the bark to figure out what species of microbes were present, and what the genetic sequences said about their ability to consumer or produce different kinds of gases. They found evidence that many of the bacteria were equipped to extract sustenance from abundant gases including methane, hydrogen and carbon monoxide.
To see how these genetic tools translated into activity, the scientists measured how much of certain gases were consumed and released by bark placed in a special sealed chamber, as well as on sections of trees encased in an airtight shell.
The results revealed that the microbes were consuming gases on an enormous scale. “This microbial activity across this massive ‘bark continent’ is potentially removing millions of tons of climate-active gases every year,” said Luke Jeffrey, a scientist at Southern Cross University who was also part of the research.
The microbes showed the most consistent appetite for hydrogen. Every species tested had microbes that consumed it. Multiply that by the world’s 3 trillion trees, and these little beasts could be sucking up 55 million metric tons of hydrogen every year, the scientists said in a posting at The Conversation.
While hydrogen isn’t directly a greenhouse gas, its presence can slow the breakdown of a methane, a potent climate-warmer. All that hydrogen disappearing into bark could translate to the equivalent of offsetting 15% of human-caused methane emissions each year, the scientists reported.
While people have talked about addressing climate change in part by planting trees, the discovery of this hidden world of bark adds a whole new dimension. It could also inform people’s calculations about which trees are the most potent climate warriors. “We now know different trees host different microbes,” said Chris Greening, a Monash University scientist. “If we can identify the trees with the most active gas-consuming microbes, they could become priority targets for reforestation and urban greening projects.”
Leung, et. al. “Bark microbiota modulate climate-active gas fluxes in Australian forests.” Science. Jan. 8, 2026.
