Northumbria Police have said a 16-year-old boy has been arrested on suspicion of causing criminal damage in connection with the felling of the Sycamore Gap tree.
The boy remains in custody and is assisting officers with their inquiries, the force said.
Northumbria Police said it believes the damage caused to the tree was a deliberate act of vandalism.
The tree is one of the UK’s most photographed and has come down overnight after being “deliberately felled”, the Northumberland National Park Authority has said.
The famous tree at Sycamore Gap, next to Hadrian’s Wall, was made famous by actor Kevin Costner when it appeared in his 1991 film Robin Hood: Prince of Thieves.
On Thursday morning, the national park authority said: “[We] can confirm that sadly, the famous tree at Sycamore Gap has come down overnight. We have reason to believe it has been deliberately felled.
“We are working with the relevant agencies and partners with an interest in this iconic North East landmark and will issue more details once they are known.”
The National Trust said in a statement: “We are shocked and desperately saddened to learn that the famous Sycamore Gap tree at Hadrian’s Wall has been felled overnight, in what appears to be an act of vandalism.
“We know just how much this iconic tree is loved locally, nationally and by everyone who has visited. We are working with our partners to understand what has happened and what can be done.”
The authority is asking the public not to visit the site, near Crag Lough, “whilst we work with our partners to identify what has happened and to make the site safe”.
A spokesperson added: “Sycamore Gap was voted English Tree of the Year in 2016 in the Woodland Trust’s awards and is much loved by people from across the world.”
The Sycamore Gap tree is probably the most photographed in the country and stands in a dramatic dip in Hadrian’s Wall.
Northumberland County Council leader Glen Sanderson expressed his shock and anger at the “absolutely terrible” incident.
“Today is a very sad day for our county. I am finding it difficult to express the shock, anger and hurt I feel at the destruction of this iconic landmark,” he said.
He added: “The Sycamore Gap tree has stood for centuries and is known throughout the world. For it to be felled in what is clearly a deliberate act is absolutely terrible and I’m sure I speak for everyone in the county when I say how upset I was when I heard the news this morning.”
The Northumberland National Park Authority’s website says the Roman Milecastle 39 is just to its left.
Sycamore Gap is looked after by both Northumberland National Park and the National Trust.
Superintendent Kevin Waring, of Northumbria Police, said: “This is a world-renowned landmark and the events of today have caused significant shock, sadness and anger throughout the local community and beyond.
“An investigation was immediately launched following this vandalism, and this afternoon we have arrested one suspect in connection with our inquiries.
“Given our investigation remains at a very early stage, we are keeping an open mind. I am appealing to the public for information to assist us – if you have seen or heard anything suspicious that may be of interest to us, please let us know.”