Some of Scotland’s most celebrated trees are used in landmark Gardens project

The simple hedge has for hundreds of years served many a noble purpose – as a land boundary, livestock enclosure and hidey-hole for creatures big and small.

Now, as a project over 10 years in the making by The Royal Botanic Garden Edinburgh finally comes to full bloom, it will perform another great service – to fight back against the biodiversity crisis and save an ancient tree species from extinction.

To be a plant on display in The Royal Botanic Gardens Edinburgh (RBGE), you have to pull your weight in terms of scientific value. Yet a one-kilometre holly hedge hugging part of the perimeter of the garden was just sitting pretty.

Martin Gardner, a conifer expert and conservationist who retired from RBGE last year, explained how the idea for a biodiverse hedge germinated in his mind almost 15 years ago.

He said: “For many years I looked at the holly hedge that surrounded the garden on three sides. Although it fulfilled its remit as a solid boundary hedge around the garden, it didn’t have any other purpose.

“The main purpose of all our plants in the garden, or any of our specialist gardens, is that they have to have some scientific reason for being there – and the holly hedge had no scientific reason at all! So I started thinking, wouldn’t it be wonderful to remove the hedge, and replace it with something that was more appropriate to our scientific remit? And I decided that we should look at yew trees.”

Yew trees tick many of the boxes that one would look for in a good hedge. While slower growing than other hedging species, its dense growth easily blocks out sound pollution, it only needs to be cut once a year, and it can thrive in both direct sunlight and shade. Yet the biggest box it ticked for Gardner was, of course, scientific. By creating the hedge from cuttings of yew trees around the world, the completed hedge would be incredibly biodiverse.

Gardner, further explained: “It is a single species called the European Yew, or sometimes the English Yew, but is has wide distribution ranging from Ireland in the west to Iran in the east. Within that large distribution, although it is the same species, genetically it will have different levels of adaptation.

“You only have to think of the difference in the weather systems you experience in Morocco, compared to what you would experience in Norway to get an idea of how different they can be. It would be like a Scottish person trying to acclimatise in the Amazon Basin, and vice versa. We’re all the same species, but we have different levels of adaptability – it’s the same in the hedge. Each cutting has different genes for adaptability.”

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The yew tree has been prized by humans from the earliest of times. In 1991, a hillwalker in the Borders found a 6,000-year-old longbow made from a yew tree in a bog. They were still being used to make weapons in the 17th and 18th Century, and as a result the Hutsul people of Ukraine and Romania were asked to pay their taxes in yews, leading to the felling of 37,800 trees over those two centuries.

Almost every part of a yew tree is poisonous, but many of its components have found its way into healing remedies throughout history. Most recently, and perhaps most significantly, it has contributed to Paclitaxel, one of the world’s most powerful and successful anti-cancer drugs.

This has added extra pressure on an already highly sought after species, with many being felled each year to meet global demand for the drug.

The centuries-long over harvesting of yews has caused population pockets of the trees across the world to shrink significantly. Thus, the RBGE hedge serves another scientific purpose, in that it will help preserve the genetic material of ancient yew trees, and save the species from outright extinction.

Gardner said: “I’ve seen dwindling yew forests in the wilds across Europe. I put together a shortlist of yew trees in countries where I thought they were threatened, and thought it would be wonderful to include them too. So our hedge is comprised of over 2,000 yew trees, both from heritage yews, and from yews from the wild.”

Using such a high number of different trees in the project will result in a slightly less neat and uniform hedge than we are used to seeing in well-looked after gardens such as the RBGE’s. Gardner is thrilled by the idea of the hedge bursting with diversity.

He said: “If you walk alongside the hedge, even from the outside of the gardens, you will be able to see it changing to a different type of green, or there may be just some sort of change in the type of the type of foliage.

“People often plant hedges because they want them to be uniform, which is fine, but that’s because it has all come from one single tree clone, and this hedge is instead incredibly biodiverse. So when people say ‘your hedge isn’t uniform!’ I say, ‘that’s biodiversity for you!’. We don’t want it to be uniform, we wanted it to look different in all different type of places, because that is part of its story.”

Many of the yew trees across the globe have incredible stories behind them. Yews have the ability to live for hundred – and in some cases, thousands – of years, meaning that they have often stood witness to some of the world’s most historically significant moments. When collecting cuttings for his hedge, Gardner took from some of the biggest yew tree mega stars that the UK has to offer.

Gardner said: “Because they have been around for a long time, some of the yew trees of Scotland are associated with incredibly famous people, whether that be Robert Louis Stevenson, John Knox, or Robert the Bruce. We’ve taken cuttings from some of these trees and included them in the hedge.

“The fact that the trees caught the fascination of these famous people a long time ago is wonderful. There is a little bit of myth and stretching of the truth with these stories – people get a little annoyed at that, but I think we should just go with it! There is no smoke without fire, there’s an element of truth to them. So I often say that our hedge is a story hedge – it’s fantastic that a proportion of the hedge includes these heritage trees with their wonderful stories.”

Gardner has written a book, The Yew Hedge: Conserving Ancient Trees from the UK and Beyond, to chart his project over the years, from when it started it 2008, until now. The book also aims to educate readers about the wonderful properties of yew trees, while also shedding light on the history of some of the UK’s, and the world’s, most significant yews. He hopes that the book, and the hedge itself, will encourage others to use his methods to protect other endangered species too.

He explained: “I think the yew tree is probably one of the most interesting trees in the world. By having this hedge here at Edinburgh, I hope that other people will do something similar. One thing that I would love to happen, maybe at the National Trust garden in Bute, or Argyll, or even Devon, is that they looked after their heritage yew trees in the area by taking cuttings and making a hedge of them for themselves.

“The reason they need to do that is because the heritage yew tree is quite threatened, which can happen due to vandalism, or they get cut down due to health and safety concerns. I really hope people will copy the idea of conservation heritages – not just in Britain, but in many parts in the world. It’s an interesting way of conserving biodiversity without taking up too much space.”

The Yew Hedge by Martin Gardner, published by The Royal Botanic Gardens Edinburgh, is out on July 18