Trees might not be acting in the way we thought – this forest fitted with pipes can tell us why

Source: BBC.com

Written by: Katherine Latham

By simulating the future atmosphere, scientists hope to understand whether trees will continue to act as the lungs of the planet.

“The oak is the queen of her domain,” says Rob MacKenzie as he gestures towards a giant towering above us. This oak tree has stood in this very spot since long before he or I walked the Earth. 

It is early winter when MacKenzie, an atmospheric scientist and director of Birmingham University Institute of Forest Research, leads me further into this small patch of woodland here in Staffordshire, England.

He treads steadily along the track, snow crunching underfoot. The low winter Sun casts long shadows, and a few birds, braving the cold, sing to each other across the forest. Autumn’s final leaves tumble to the ground – where they land not on the floor, but in nets. Because this is no ordinary forest. 

Where roots tangle across the earth, pipes and wires intertwine. This forest has plumbing. Silhouetted oak, birch and sycamore trees stand shoulder to shoulder with towering metal frames supporting drainpipes, which reach up to the very tops of the trees.

MacKenzie and his colleagues have sent this quiet forest just outside Birmingham into the future – in a manner of speaking. They have pumped carbon dioxide (CO2) around the mature oak trees here in order to simulate the atmosphere that is expected to swathe planet Earth by the year 2050.

This small wooded area, close to an urban metropolis, is not the only one getting a blast of the future with artificially elevated levels of CO2. Researchers across the globe, from Australia to the Amazon rainforest, are experimenting on forests in a bid to better understand the role trees play in keeping the Earth cool. Their findings could transform our understanding of how the forests of the future will respond to climate change. 

MacKenzie and his colleagues have been running their experiment for seven years to date, and the results have surprised them. Contrary to some previous analyses, their study suggests that trees can actually absorb more carbon as they age. It’s a finding that highlights the immense importance of mature, temperate forests in terms of climate regulation.

What’s more, for the first time, MacKenzie and his fellow forest-watchers have also shown that microscopic organisms living on these trees capture methane, another greenhouse gas harmful to the atmosphere. “[We] found the trees are providing another unexpected service for us,” says MacKenzie. “The canopy hosts microbes, and these microbes eat the methane. There are lots of reasons to nurture forests.

Earth’s natural greenhouse effect – whereby gases such as CO2 and methane absorb the Sun’s heat as it radiates back from the Earth’s surface, trapping it in the atmosphere – is vital for life as we know it. It helps to keep the average global surface temperature comfortably above freezing.

Carbon sinks, meanwhile – such as forests, oceans and soils – absorb CO2 from the atmosphere, preventing the Earth from overheating due to this greenhouse effect. Our climate has existed this way for millennia, in a delicate state of balance.

Vast swathes of the world are about to change, or are indeed changing – Rob MacKenzie

However, with rising greenhouse gas emissions from human activities, the amount of those gases absorbed by nature has increased, too. It has made plants grow faster, a process known as CO2 fertilisation. Natural carbon sinks currently absorb roughly half of all human-produced carbon emissions, according to estimates. But experts warn we may be on the verge of tipping the balance – with both ocean and land sinks showing signs of struggling to keep up. 

In fact, extreme heat and drought, forest fires and deforestation, land use change, melting permafrost and warming oceans could all lead to carbon sinks such as forests transforming into carbon sources – meaning they emit more CO2 than they absorb.

“Climate change is happening faster, to the best of our understanding, than the natural adaptability of every ecosystem,” says MacKenzie. “Bogs are turning into scrubby forests, scrubby forests are turning into lakes. It’s a system shift. And forests are vulnerable the same way as every ecosystem is.”

Tree species themselves are also increasingly at risk. According to the 2024 update of the International Union for Conservation of Nature’s Red List, over one-third of the world’s trees are now in danger of extinction due to global warming, deforestation and invasive species.

So, can we rely on trees to continue keeping the Earth cool?

In Staffordshire, MacKenzie and his colleagues are racing to better understand the role trees play in regulating the Earth’s climate. “The team are out here every day,” says MacKenzie. “They care deeply about what they do. Every weekday, and sometimes the weekend too.” 

Their woodland experiment involves studying how elevated CO2 affects a huge range of processes – from forest carbon flows, nutrient cycles and water use to overall biodiversity and ecosystem structures. This type of experiment is called free-air CO2 enrichment, or Face.

The excess CO2 comes from the anaerobic digestion of waste food in two massive tanks just outside the project headquarters, at the edge of the forest. Tubes transport the CO2 across the forest floor, where eight-storey-high drainpipes reach to the very top of the canopy. These pipes, hidden among the tree trunks and supported by metal towers, have simple holes drilled into them, which allow the CO2 to escape into the atmosphere. The gas is present for about a minute, says MacKenzie, before it either gets absorbed by the trees or dissipates into the surrounding air.

Meanwhile, strategically placed stations collect data on everything from soil composition to insect populations and more, helping the researchers understand the impact of elevated CO2 on the entire ecosystem.

The results of the experiment so far, show that mature forests exposed to elevated levels of CO2 not only continue to capture carbon as they age, they also store it for longer than trees exposed to lower levels of CO2, by growing extra bark.

When exposed to the volume of CO2 that scientists estimate will be present in our atmosphere by the 2050s, the wood production of the trees increased by 10%. This is especially significant since trees can store carbon in their wood for decades. Their leaves or roots, in contrast, decay more quickly and release their carbon back into the atmosphere.

These findings help to reveal the important role that mature forests will play as carbon stores and natural climate solutions in the coming decades. The fact that the microbes living in the canopies of these mature oaks also consume methane is an added bonus to mitigating the effects of human emissions. This process was first discovered in 2024 right in this patch of English woodland and it means that forests are even more important in the fight against climate change than scientists previously understood.

Concentrations of methane in the atmosphere have been rising rapidly for decades now. This greenhouse gas has resulted in about a third of climate warming since preindustrial times.

Methane is many more times as potent as CO2, in terms of its ability to trap heat in the atmosphere. But while CO2 can last for hundreds of years, methane has an atmospheric lifetime of roughly one decade. This means that removing methane from the atmosphere can have rapid effects – and if removal is enhanced, it could be a “quick climate win“.

The findings from Staffordshire indicate trees take up around 25 to 50 million tonnes of atmospheric methane each year, making them 7-12% better for climate than they are currently credited for.

Elsewhere in the world, other experimental forests are also starting to yield data.

Launched in 2023, in one of the largest open-air laboratories in the world, the first CO2 experiment conducted on a tropical forest is in its early stages.

The Amazon is home to more than 10% of all terrestrial biodiversity and stores an amount of carbon equivalent to around 20 years of global CO2 emissions. But scientists warn that warming temperatures, extreme droughts, deforestation and fires mean the Amazon forest system could “soon reach a tipping point, inducing large-scale collapse“.

In a patch of mature rainforest in the heart of the Amazon near Manaus, Brazil, researchers are pumping predicted future atmospheric levels of CO2 over the trees using the same Face technology as in Staffordshire. They hope to better understand how the world’s largest rainforest will respond to climate change.

“We are measuring components of the forest productivity”, says Laynara Lugli, a tropical ecologist studying the effects of climate change on soil-plant interactions at the Technical University of Munich. “So, leaves growing, stems growing, roots growing. We are very interested in physiological patterns – looking deep into the leaves [to see] how the photosynthetic capacity is changing. 

Lugli is especially interested in what happens below ground during her CO2 experiment: “Are [the roots] getting water? Are they getting nutrients? [Is the] symbiosis with fungi changing? How does this affect the whole functioning of the forest?”

She and her colleagues are also investigating how climate change will affect the biodiversity of the rainforest, and how it might impact this habitat’s ability to provide food, wood, medicines and even rain. 

While different species show a range of responses, says Lugli, initial findings indicate that elevated levels of CO2 here could lead to plants increasing the growth of their leaves and stems. Below ground, roots “grow longer and thinner”, she adds, allowing trees to cover greater distances in order to find the nutrients they need. This favours fast-growing but short-lived species with lower wood densities, which also tend to be less resistant to drought.

The whole life cycle speeds up, says Lugli. “What’s the fate of the carbon? Maybe it’s going to be respired back to the atmosphere and not be stored in the soil.”

Back in the quiet Staffordshire countryside, MacKenzie agrees. “There is no amount of reforestation that we could do that would allow us to keep burning fossil fuels at the rate that we’re burning them. There certainly is a role for forests – but it’s not a silver bullet.”

But, he asserts, the work he and his colleagues are doing is “a game-changer”. Not least because it highlights the impact that temperate woodlands could have on the future climate.

That, says MacKenzie, is something we are in danger of forgetting.