FROM the stately grandeur of Nuneham Courtenay to the gargantuan giant redwoods of the Californian coast, two tree climbers from Oxford University's Harcourt Arboretum have recently returned from international missions to collect seeds from some of the widest, tallest and oldest trees on the planet.

This March, Luke Rowland's and Guy Horwood's expeditions will be retold into a new tree trail at Harcourt, where they will lead guided tours recounting their adventures.

They gave environment reporter Pete Hughes a sneak preview of those tours and revealed what it feels like to be on top of the world.

LUKE Rowland hauled himself to the top of the Brewer's Spruce tree and looked around.

From his perch on top of Iron Mountain, the former Didcot schoolboy could see for hundreds of miles across the rocky Oregon landscape.

"It was amazing," he recalls, "thinking I had been given special access to this amazing view."

The reason Mr Rowland, 27, had trekked for countless hours then climbed 30m up this tree may seem humble: he was collecting cones.

The longer explanation is that the Harcourt Arboretum tree climber had been recruited for an international mission to collect seeds from some of the world's most important trees and bring them back to the UK's world-famous Millennium Seed Bank.

Alongside him were plant experts from Kew Gardens, which runs the seed bank, and staff from the US Forestry Service.

That particular day, he admits, was something of a saga.

"One of the chaps we went out with was a geneticist from the forestry service: he had scouted a lot of the sites, but this was one of the ones he hadn't visited," said Mr Rowland.

"He only knew the population was there through some literature so we walked up the side of this mountain and it was looking as though we just weren't going to find it.

"We got to the top, he got his binoculars out and spotted it 300m away across the mountain side, so we had to tramp back down the mountain to collect the climbing gear then go all the way back up."

At the other extreme of his two-week expedition down the US western seaboard from Canada to southern California, Mr Rowland and the team raced against time as the heat from late summer sun threatened to destroy precious pine cones before they could reach them.

He said: "Sometimes I got to the top of trees and the cones would just crumble in the your hand: they disintegrate in the heat and the seeds have little wings on them so they just fly off for kilometres."

The challenge for the team was vast: in 16 days they had been asked to collect 20,000 to 40,000 viable seeds per tree species.

For the former St Birinus pupil that meant scaling up to 20 trees a day and picking thousands of cones.

Mr Rowland then had to spend the long evenings cleaning every single cone and delicately packaging them all ready for transport back to the UK.

Days began at 6am and sometimes didn't finish until 1am.

His expedition in September was the sequel to a similar adventure made by his fellow Harcourt arborist Guy Horwood in 2015.

On that trip, Mr Horwood had the slightly daunting task of collecting pinecones from the oldest trees in the world: the gnarled and knotted bristlecone pines.

Many of these trees, which only grow at altitudes of 3,000m up in the western United States, are more than 4,000 years old: they started growing during the time of the Egyptian Pharoahs.

One of them has been dated at 5,066 years old, making it the oldest known single living organism in the world.

Mr Horwood, 27, said: "It's hard to describe the feeling when you're standing next to trees that are that old, it is awesome.

"They grow in a very weird environment – you have to go to the middle of nowhere then drive up a mountain to these very surreal forests."

Mr Horwood also had to climb some of the tallest trees in the world, the famous west coast redwoods, using ropes to haul himself up more than 100ft, branch by branch, sometimes just to find out whether there were any viable cones up there.

The Sparsholt college graduate, who now lives in Henley, said: "As a tree person you can't get much better than the west coast of America, that's our Mecca.

"They've got the biggest, the oldest and the largest trees in the world.

"They are incredible trees and not many people get the opportunity to climb them legally."

The tens of thousands of seeds Mr Horwood and Mr Rowland collected are now being weighed and X-Rayed at the Millennium Seed Bank, before they are put into storage in one of the most important libraries in the world.

But in March, the arboretum will unveil a new photography trail which will allow visitors to experience some of the American adventures themselves.

The 11 huge, high-resolution photo boards dotted around the site will link individual arboretum trees with trees the adventurers met on their expeditions.

One board in front of the arboretum's oldest tree – a 400-year-old oak – will compare it to the oldest tree in the world – the bristlecone pine of Oregon.

Both tree climbers will also be giving guided walks along the trail recounting some of their adventures shimmying up the tallest trees on the planet and plucking pinecones off the oldest living organisms known to man.

But more than that, just a few of the seeds they collected will make their way to Harcourt, where they will do a lot more than sit in storage: the tiny vessels will be propagated and grown into modest English versions of their giant American parents.

And with a little love and care, in 150 years' time they will be gazed up at by the awestruck great grandchildren of today's visitors.

Mr Horwood muses: "It nice to think we're continuing that heritage and helping with conservation – there is a lot more to it than just planting a tree."

Mr Rowland, who now lives in Denchworth near Wantage, agrees.

He said: "Because I am so passionate about trees and wildlife I want people to come in and take something away from the arboretum and be inspired.

"Even if they learn one small thing they didn't know before, that's brilliant."