The world's oldest tree may have been standing for centuries when the first boulders were erected at Stonehenge, new research suggests.
The ancient giant, an alerce (Fitzroya cupressoides) known as the "Gran Abuelo" (or great grandfather in Spanish) that towers over a ravine in the Chilean Andes, may be roughly 5,400 years old, a new computer model suggests.
If that date can be confirmed, it would make the Gran Abuelo nearly 600 years older than the current official record holder for world's oldest tree, a Great Basin bristlecone pine (Pinus longaeva) in California known as "Methuselah".
However, the alerce's exact age is still somewhat contested, because confirming that requires analysis of the tree's rings – a method known as dendrochronology, and the gold standard for determining a tree's age – and that data is currently incomplete.
The underlying data for the model has not yet been publicly released or submitted to a peer-reviewed journal.
Whatever its age, the tree is in peril and needs to be protected, said Jonathan Barichivich, a climate and global ecology scientist at the Climate and Environmental Sciences Laboratory in Paris, and the researcher who created the model.
"It's really in poor condition because of tourism," and the tree has also been affected by climate change, Barichivich told Live Science.
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The Gran Abuelo, a conifer that rises 196 feet (60 meters) above the misty forest floor in Alerce Costero National Park in Chile, was initially thought to be roughly 3,500 years old. But scientists had never analyzed its age systematically, Barichivich said.
"We wanted to tell the story of the tree with the only aim to valorize it and protect it," Barichivich said.
So in 2020, Barichivich and his colleague Antonio Lara, a forestry and natural resources professor at the Austral University of Chile, used a nondestructive technique to drill a tiny core from the tree, which captured 2,465 years' worth of tree rings.
The borer, however, could not reach to the center of the tree's 13-foot (4 m) diameter, which means that many of the alerce tree's growth rings could not be counted.
To account for the remaining years of growth, the team developed a mathematical model that took into account how F. cupressoides grows at different rates, from a sapling to a mature tree. The model also incorporated variations in growth rate based on competition and fluctuations in environment and climate.
The team then used the model to simulate the tree's growth trajectory 10,000 times, Barichivich said. Those simulations gave a range of predicted ages for the Gran Abuelo.
The model estimated the tree was most likely around 5,400 years old, Barichivich explained. The absolute oldest the tree could be was 6,000 years; there was about an 80 percent chance the tree was older than 5,000 years; and all of the simulated growth trajectories predicted it was at least 4,100 years old, he said.
"Even if the tree was a very fast grower, for all that size, it cannot be younger than that," he said.
Another factor suggests that the tree is very old: a biological law known as the growth-lifespan tradeoff, Barichivich added. That tradeoff suggests that slow-growing species tend to live longer. And alerce trees grow incredibly slowly – slower even than other long-lived species such as giant sequoias (Sequoiadendron giganteum) or Great Basin bristlecone pines, he said.
However, some tree-dating experts told Science Magazine that they were wary of using modeling data to estimate a tree's age.
"The ONLY way to truly determine the age of a tree is by dendrochronologically counting the rings and that requires ALL rings being present or accounted for," Ed Cook, a founding director of the Tree Ring Laboratory at Columbia University's Lamont-Doherty Earth Observatory in New York, told Science Magazine in an email.
While the tree has survived for thousands of years, its future is in doubt, Barichivich said.
The ancient tree has been encircled by a narrow platform walkway that is crushing its last living roots, he said, and the myriad tourists that come to see the tree every year do further damage when they walk on it.
Climate change and the attendant 10-year drought has also damaged the majestic alerce; a second tree growing from the top of the towering giant is now dying, he said.
To protect the Gran Abuelo from further damage, Barichivich and his colleagues have proposed placing a veil of netting 10 feet (3 meters) high around the tree to prevent people from getting too close. They also recommend moving the walkway much farther away from the tree's ancient root system, he told Live Science.