Roughly 5,400 years ago, a tiny seed sprouted from the forest floor in central Chile. As it survived fires and logging, the Patagonian cypress grew to become one of the largest trees inside Alerce Costero National Park, eventually ballooning to more than 13 feet in diameter.
Now, a researcher believes the tree—known as Alerce Milenario or Gran Abuelo, the “great-grandfather” tree—is likely the oldest in the world, reports Science’s Gabriel Popkin.
Chilean environmental scientist Jonathan Barichivich, working at the Climate and Environmental Sciences Laboratory in Paris, has estimated that the tree is 5,484 years old. If Barichivich's unique process for calculating the tree’s age is correct, that would make Alerce Milenario much older Methuselah, a 4,853-year-old bristlecone pine in California currently thought to be the world’s oldest tree.
Researchers typically calculate a tree’s age with a process known as dendrochronology, which involves counting the number of rings in the tree’s trunk. While a tree is still alive, they do this by boring into the trunk and examining a core sample; they may also take a sample from the roots and use carbon-dating techniques to determine its age.
But Chile’s Alerce Milenario is too wide for a standard borer to reach its center, and the roots of the ancient tree have become too fragile with its advanced age, so Barichivich had to take a different approach.
"The objective is to protect the tree, not to make headlines or break records," Barichivich tells Newsweek’s Jessica Thomson. “It's not the point to make a big hole in the tree just to know that it's the oldest. The scientific challenge is to estimate the age without being too invasive to the tree."
In 2020, Barichivich and collaborator Antonio Lara, a forest and natural resources scientist at the Austral University of Chile, took a partial core sample from the tree and counted 2,400 growth rings. Then, they used statistical modeling techniques, informed by known growth rates of that species of tree, to extrapolate further. Looking at complete core samples from other alerce trees and studying how environmental factors can affect tree growth, they created a model that calculated the probability the tree had reached certain ages.
Based on that model, there’s an 80 percent chance the tree has lived more than 5,000 years, with an overall age estimate of 5,484 years. Barichivich was shocked: He’d expected the tree to be around 4,000 years old.
The researchers have not published their findings, but Barichivich says he plans to submit a paper to an academic journal in the coming months; they’ve also presented their work at meetings and conferences. Still, some dendrologists and plant scientists are unconvinced by their methods and their conclusion.
“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 climate scientist who specializes in dendrochronology at Columbia University, tells Science.
Skepticism aside, Barichivich says his age estimate is important because it may help the tree get the federal protection it deserves. Visitors to Alerce Costero National Park can walk right up to the tree and, though there’s a platform in place that’s meant to protect the roots, people still clamber all over them. Not only does that harm the ancient tree’s roots, but it also compacts the soil, which can make water and nutrient uptake difficult for Gran Abuelo. The tree is also stressed from an increasingly dry climate, which has made it harder for the roots to soak up water. Barichivich estimates that only 28 percent of the tree is still alive, per Newsweek.
Since he grew up on his family’s Indigenous land near the tree, Barichivich feels a special connection to Alerce Milenario—and he hopes his study of the tree’s age will help other people feel that way, too.
"To me, this tree is like a family member,” Barichivich tells Newsweek.