Trees may not act the way we thought

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

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

He walks steadily along the path, the snow crunching underfoot. The low winter sun casts long shadows and some birds brave the cold and sing to each other through the forest. The last leaves of autumn fall to the ground – where they do not land on the floor, but in webs. Because this is no ordinary forest.

Where roots tangle through the soil, pipes and wires become intertwined. This forest has plumbing. Silhouetted oak, birch and sycamore trees stand side by side with tall metal frames that support the drainage pipes, which reach up to the treetops.

MacKenzie and his colleagues have sent this quiet forest outside Birmingham into the future – so to speak. They have pumped carbon dioxide (CO2) around mature oak trees here to simulate the atmosphere expected to cover planet Earth by 2050.

This small forested area, close to an urban metropolis, is not the only one receiving a future blast with artificially elevated CO2 levels. Researchers around the globe, from Australia THE Amazon rainforestare experimenting in forests in an effort to better understand the role trees play in keeping the Earth cool. Their findings could transform our understanding of how future forests will respond to climate change.

MacKenzie and his colleagues have been conducting their experiment for seven years to date, and the results have surprised them. On the contrary to some previous analysestheir study suggests that trees may actually absorb more carbon as they age. It is a discovery that highlights the tremendous importance of mature, temperate forests in terms of climate regulation.

Furthermore, for the first time, MacKenzie and his fellow forest observers have also shown that the microscopic organisms living in these trees methane captureanother greenhouse gas harmful to the atmosphere. “[We] found that trees are providing another unexpected service for us,” says MacKenzie. “The canopy hosts microbes, and these microbes eat the methane. There are many reasons to feed forests.

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

Carbon chokesmeanwhile – 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.

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

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

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

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

The excess CO2 comes from the anaerobic digestion of food waste in two massive tanks outside the project headquarters, on the edge of the forest. The pipes transport CO2 across the forest floor, where eight-story drainage pipes reach the top of the canopy. These tubes, hidden between tree trunks and supported by metal towers, have simple holes drilled in them that allow CO2 to escape into the atmosphere. The gas is present for about a minute, MacKenzie says, before it is either absorbed by the trees or dispersed into the surrounding air.

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

of the results of the experiment so farshow that mature forests exposed to high CO2 levels not only continue to sequester carbon as they age, but also store it for longer than trees exposed to lower CO2 levels by growing additional bark.

When exposed to the volume of CO2 that scientists estimate will be present in our atmosphere by the 2050s, Tree wood production increased by 10%. This is particularly important as 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 reveal the important role that mature forests will play as carbon sinks and natural climate solutions in the coming decades. The fact that the microbes living in the tents of these ripe oaks also consume methane it is an added bonus for mitigating the effects of human emissions. This process was first discovered in 2024 in this very part of English woodland, and it means that forests are even more important in the fight against climate change than scientists previously realised.

Methane is many other times as powerful 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 approx a decade. This means that removing methane from the atmosphere can have rapid effects – and if the removal increases, it could be a “quick climate win“.

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

Launched in 2023, in one of the world’s largest open-air laboratories, the first CO2 experiment conducted in a rainforest is in its early stages.

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

In one piece mature rainforest in the heart of the Amazon near Manaus, Brazil, researchers are pumping predicted future atmospheric levels of CO2 onto 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 the components of forest productivity,” says Laynara Lugli, a tropical ecologist who studies the effects of climate change on soil-plant interactions at the Technical University of Munich. “So leaves grow, stems grow, roots grow. We’re very interested in physiological patterns—looking deep into leaves [to see] how the photosynthetic capacity is changing.

Lugli is particularly interested in what happens underground during her CO2 experiment: “Are [the roots] taking water? Are they getting nutrients? [Is the] does the symbiosis with fungi change? How does this affect the entire functioning of the forest?”

She and her colleagues are also investigating how climate change will affect the biodiversity of tropical forests and how it may affect the ability of this habitat to provide food, wood, medicine and even MIS.

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

The whole life cycle is accelerated, says Lugli. “What is the fate of the carbon? Maybe it will go back into the atmosphere and not be stored in the soil.”

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

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

This, says MacKenzie, is something we risk forgetting.

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