Martin Gardner: Hedge your bets over Botanic's garden plans

The Fortingall Yew, which is considered to be possibly the UKs oldest tree, has contributed to the new Royal Botanic Garden hedge in Edinburgh. Picture:

As July and August witness frantic activity by gardeners to control the year’s vigorous growth of garden hedges it is easy to appreciate how these living boundaries provide privacy, help demarcate territory and are mostly maintained to look attractive. But there are hidden depths to our hedges. Apart from these practical functions – and importantly providing valuable habitats for wildlife such as nesting birds – hedges could have further beneficial roles and can contain the necessary information to save lives.

Plants are our food, drink and medicine and we cannot live without them. Here, at the Royal Botanic Garden Edinburgh’s (RBGE) Inverleith site, we study plants and encourage public engagement with the natural world. At the same time we are challenged to maximise every opportunity in our limited 32 hectares to efficiently accommodate the “hard fought” plant collections from all around the world.

So, charged with the life-saving task of conserving plant biodiversity in the face of global environmental change and mass extinctions, as scientists and horticulturists we work closely together to ensure that the plants we grow are relevant to the research we carry out. To do this we must employ novel ideas and no area of the Garden is considered out of bounds in order to facilitate our Living Collection.

To this end we have turned our attention to the perimeter hedge that contains the Garden continuously on three sides.

Until recently the 900m length hedge comprised mostly common holly (Ilex aquifolium) which only had a utilitarian role of forming a green linear demarcation between the Garden and the outside world. It had no useful scientific purpose. The replacement hedge, which we started planting in 2014 and is due for completion over the next two years, has provided a unique opportunity to cultivate over 2,000 new trees of the European yew (Taxus baccata).

This has transformed a boundary that had originated from a single clone to a creation of conservation significance containing a rich library of genetic information.

Collected from 16 European countries – such as Albania where only a handful of trees survive, and conversely from the great forest at Kingley Vale, Sussex, famed as being the finest yew forest in western Europe – it also contains genetic material from 30 heritage yews around the British Isles, especially from the churchyard yews that often predate the buildings and originate from long-vanished forests. Why should this be important? Don’t let us forget that only relatively recently the anti-cancer drug taxol was discovered in the yew tree and has revolutionised cancer treatments.

Growing plants as hedging dates back to the 16th century, when they were first used as a means of containing livestock. In more recent years they have taken on a new function by acting as conservation corridors for wildlife. The link between hedges and conservation, therefore, is not unprecedented. At a time when we are constantly bombarded with grim news of yet another British tree succumbing to a harmful exotic pathogen there are more good reasons why hedges are important. Since the the first notable tree to be affected was the elm in the late 1960s, some 25 million trees have perished in the UK. Fortunately for us, around the country we can find examples of conservation hedges being used to conserve the species and help buy time until a cure for the disease can be found

This Noah’s ark approach is an excellent model for how we can cram into a relatively small space important genetic information that could be crucial for the survival of a plant species.

This example is now being adopted by other gardens in Britain and as far afield as Peru, where threatened species are being conserved in a series of hedges. The International Conifer Conservation Programme, based at RBGE, is aiming to adopt this model for some of the world’s 28 Critically Endangered conifers species, many of which are represented by fewer than 100 individual plants. The ambition is to extend the hedge theme to include conservation mazes, so the call is out!

Garden hedges can be multifunctional but if used to hold a variety of genetic information they may lose their uniformity. Once the yew hedge at RBG Edinburgh is mature I look forward to being asked the question: “Why, unlike normal yew hedges, is this one not very even in growth, colour and texture?” My simple retort will be “Ah, but that’s biodiversity for you!”

• Martin Gardner is co-ordinator of the Royal Botanic Garden Edinburgh’s International Conifer Conservation Programme