By Sarah Mukherjee
Environment correspondent, BBC News
The public is being asked to help the Woodland Trust charity create a map of the UK's ancient woodlands.
Conservationists say Britain has more ancient trees than any other nation in northern Europe. The yew at Fortingall in Perthshire is thought to be the oldest.
The Fortingall Yew is as old as Stonehenge
What is conceivably Europe's oldest living thing is looking a bit green around the edges.
But that is a good thing, and much to the relief of those charged with its care.
Because when the Fortingall Yew in Scotland produces young, fresh leaves, it means it's adding another year to the thousands it has already been on this earth.
About 5,000, to be precise. A sapling when Stonehenge was created, 3,000 years old when the Romans came to Britain, a survivor from Pyramids to iPod.
"We are aware that it's a great responsibility" says Dr Gordon Stark, the session clerk at Fortingall Kirk.
"There's a very large bit of the circumference missing. It once stood 56ft in diameter, but souvenir hunters and young men who used to hold bonfires inside the hollow tree have all taken their toll.
"It's now got only a few bits left, but they are still alive and sprouting"
The tree lies inside the village kirkyard, framed by a peaceful valley, lulled by the sound of lowing cattle and bleating sheep.
The yew tree has been known for its longevity, and was also regarded in some pre-Christian traditions as a tree of great spirituality.
"Before Christianity came to Scotland in the 7th Century the people who were here had known this tree for a few thousand years and held it in great reverence," says Dr Stark.
"It's probably quite natural that when the Christian missionaries came here from Iona, they settled and built their church quite near here, close to the tree that local people no doubt respected and treated as special."
Conservationists at the Woodland Trust say they realise such an arboreal Methuselah is not the sort of thing you find in every bit of woodland - but nevertheless, there are treasures to be found.
As we take a walk in nearby woodland in Glen Lyon, Andrew Fairburn of the Woodland Trust explains what the purpose of the Ancient Tree Hunt is.
"It's to create an online record of ancient trees right across the UK. There is no register officially for these trees at present, but we think they're nature's equivalent of historical monuments, and we should treat them as such," he says.
"Some other countries in Europe protect individual trees as nature reserves, because an ancient tree can support hundreds of different species, mosses, lichens, birds and small mammals."
So what should we be looking for?
"If it's old, fat and gnarled then you should record it," Mr Fairburn says.
"An example is, if you're looking at an oak tree, if you and two friends can hug the tree standing finger to finger, then that's the sort of width we're looking for.
Politicians and environmental groups are often disparagingly referred to as "tree-huggers" but the Woodland Trust wants you to do just that - and help protect our living historic monuments at the same time.