The world-famous Sycamore Gap tree was at least 100 to 120 years old when it was illegally felled, experts have said.
The exact age of the tree on Hadrians Wall in Northumberland has been a matter of debate, with the date of its planting put in the late 1800s.
Now Historic England experts have narrowed the minimum age range down by counting the trees rings in a cross-section of trunk, with the wood considered to be in "good condition".
Two men from Cumbria were each jailed for more than four years for chopping down the tree on a stormy night in September 2023.
The tree was believed to have been planted by the then-landowner John Clayton between 1860 and 1890 to be a "feature in the landscape".
Adam Carruthers and Daniel Graham sparked global outrage when they filmed themselves felling it with a chainsaw in the early hours of 28 September 2023.
Historic England said their dendrochronological (tree-ring counting) investigation was the first research to be carried out into the age of the sycamore tree, which was formed by two stems that "fused together" when they were about 30 or 35 years old.
By counting the sequence of rings, the researchers arrived at an estimated overall count of 100 to 120 growth rings, a spokesman said.
Each ring typically indicated one year of growth suggesting the tree was at least 100 to 120 years old, he added, with the section having been examined at Fort Cumberland Laboratories in Portsmouth.
The section had stood 1m (3ft) off the ground and covered the two main stems of the tree, with the pale white or cream-coloured wood recorded as being in "good condition".
While many of the rings were "relatively clear", others were less distinctive which made it "challenging" to complete a precise count, the spokesman said.
The section of wood would be preserved for further and more detailed analysis, including the possible use of advanced imaging techniques by the University of Exeters Digital Humanities lab to provide a "more accurate count", Historic England said.
Zoƫ Hazell, senior palaeoecologist in Historic Englands Investigative Science team, said it had been a "privilege" working on "such an iconic tree" and "being able to contribute to our knowledge and understanding of its history in the landscape".
She said the section would be preserved in Historic Englands National Wood Collection to be "kept safe for the nation".
Cathy Tyers, the teams dendrochronologist, said: "I hope that this research adds further to its fascinating story and contributes to its remarkable legacy."
Ms Tyers, whose usual work was on buildings and archaeological sites, said there were "challenges" due to the ring boundaries of sycamores being "less obviously defined" than other tree species and the "comparative scarcity of existing reference data on historic sycamore trees".
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