Saving Anne Frank's chestnut: tree of hope or diseased threat?

For Anne Frank, the majestic chestnut tree she gazed on from the attic window was a source of comfort as she hid from the Nazis. For today's visitors to the elegant Amsterdam terrace house, it cuts a rather more forlorn figure.

The replica black-out curtains mean you cannot even see the tree as Anne did from the Secret Annex. The only public view from a room in the adjoining museum reveals a specimen past its prime, its crown heavily lopped and the remaining gnarled branches swinging precariously, buffeted by gusts off the North Sea.

Everyone agrees the 150-year-old tree is dying, eaten away from the inside by two rapacious forms of fungus and attacked from the outside by a leaf-curling moth. Many people, including its private owner, wanted to put it out of its misery, but those lobbying for a stay of execution have won the day. Yesterday the Support Anne Frank Tree foundation (Saft) formally took custody of the tree and is now racing to erect a form of flora life support.

"The Anne Frank tree is not just a tree," said Professor Arnold Heertje, a leading member of the Saft foundation. "It's one of the symbols of the Holocaust, a reminder of the attempted destruction of the Jews."

The foundation's plan is to build a steel frame, which Professor Heertje likens to a corset, designed to prevent the 30-tonne, 22ft tree crashing to the ground or, more worryingly, into the Secret Annex. The construction, which consists of two metal rings attached to a firmly anchored tripod, is expected to cost around €70,000 (£53,000) to build and set up and then €10,000 to maintain every year after that. And the clock is ticking to secure the funding and get the frame in place. Amsterdam council has imposed an end-of-May deadline because by then, the tree will have blossomed and sprouted leaves, and the trunk might not be able to support the additional weight.

The saviours of the horse chestnut make much of the three occasions in her 336-page diary when Anne Frank mentions the tree. "I go to the attic almost every morning to get the stale air out of my lungs," she wrote on Wednesday 23 February 1944. "This morning when I went there, Peter was busy cleaning up... The two of us looked out at the blue sky, the bare chestnut tree glistening with dew, the seagulls and other birds glinting with silver as they swooped through the air, and we were so moved and entranced that we couldn't speak."

Anne's father, Otto – the only one of the eight residents at 263 Prinsengracht to survive the concentration camps where they eventually ended up – recalled his surprise at discovering his daughter's interest in nature after reading her diary for the first time.

"How could I have suspected that it meant so much to Anne to see a patch of blue sky, to observe the gulls during their flight and how important the chestnut tree was to her," he said in a speech in 1968. "But she longed for it during that time when she felt like a caged bird. She only found consolation in thinking about nature."

There is no doubting the tree's symbolism. Nor its global allure. Each day hundreds of visitors leave a message on a leaf in Anne's virtual tree on the official website. And people are willing to pay for a real-life piece of the history too. One enterprising neighbour decided to sell a chestnut, billing it as a last chance to "Grow your own Anne Frank tree anywhere" and after a four-day bidding war on eBay, it sold for about £5,000.

But despite the universal appeal of the horse chestnut, there are those who would say its defenders are barking up the wrong tree.

Even with the new steel frame, the tree is only expected to stand for another 15 years at most, by which time it will have run up costs of more than €200,000 . Its leaves already turn prematurely brown in summer because of the leaf miner moth. And although some optimistic protectors still talk hopefully of being able to find a permanent cure for the tinder polypore and honey mushroom fungi gobbling away at the trunk, sonar images taken over the years suggest otherwise.

The blue tint of the dead wood has rapidly gained ground, and at the last count, only 29 per cent of the tree was living wood. Normally trees in the Netherlands are cut down when this level hits 33 per cent.

"The tree in its old form, if it could have been kept alive, would have been fantastic," said Hans Westra, the director of the Anne Frank House, who has seen the tree almost every day for the 30 years he has worked for the museum. "But that's not possible. What we will have in a couple of years is a tree that has been cut so much that it's unrecognisable as her tree."

And it's not as if the alternative to extending the life of the tree is simply to leave a gaping hole. Six genetically identical specimens, grown from grafts from the mother tree, are being nurtured in northern Holland and are already 7ft high, ready to replace the original if it should ever be felled.

What's keeping Mr Westra awake at night though is the possibility of an unplanned fall. "The most important thing is that the tree cannot be allowed to be a danger to the Secret Annex," he said. "I don't feel 100 per cent safe but I have to accept the word of the experts."