Planting Elms in the British Countryside
Elms are traditional trees of the British countryside. The English elm, Ulmus procera, was a characteristic tree of hedgerows in England until it was decimated by Dutch Elm Disease (DED) in the 1970s. English elm is a single clone so all English elms are genetically identical. This elm doesn’t produce viable seed so it was propagated from suckers. It continues to thrive as sucker growth in hedges where the mature trees have long gone.
The typical elm of woodlands is the wych elm, Ulmus glabra. Wych elm is more tolerant of DED and still thrives in many woodlands especially, but not exclusively, in the North and West. Unlike English elm, the wych elm rarely produces sucker growth but it does regenerate from seed, although it is often difficult to find a reliable source.
Native sources of wych elm generally grow as medium sized trees with a tendency to fork. This source is ideal for planting in new woodlands as an understorey species; it will shade the woodland floor without competing for light with the taller trees in the canopy. By contrast, wych elm from central Europe have evolved in dense broadleaved forests where they have had to grow fast and straight to survive the competition. They have been known to reach 37 metres in height and their trunks up to 1.5 metres in diameter. Most of the best European wych elms have been felled to make high quality veneers and it is seldom planted now for fear of Dutch Elm Disease.
A third species of elm is the smooth-leaved elm, Ulmus carpinifolia or Ulmus minor. It is common in continental Europe but mainly restricted to East Anglia and surrounding counties in England. It suckers well and produces viable seed. It hybridises very easily with wych elm to produce a range of forms commonly known as Dutch elms, Ulmus x hollandica. Cornish and Huntingdon elms are also thought to be the result of crosses between smooth-leaved and wych elms.
The white elm, Ulmus laevis, is not thought to be native to Britain but it is widely found in Europe from France through to Russia. White elm produces large quantities of viable seed in May that germinates immediately and grows very fast. It is the least susceptible of all the elms to DED.
Unfortunately, despite their importance in the British countryside, elms are seldom included in new plantings nowadays. The chief reason for this is the perception that our native elms will inevitably succumb to DED so there is no point in planting them. If seed is collected from healthy elms that have survived for 40 years of DED then there is a good chance that the progeny will also inherit some of that disease resistance. Every young elm grown from seed is genetically unique, so these trees should be widely planted throughout the British countryside. This will ensure that more strains resistant to DED will thrive and spread. By planting an elm that suckers, even if the original tree dies (by no means certain) its suckers will continue to supply the ecological functions of elm in the woodland ecosystem.
Elms should form no more than 5% of a new planting scheme and be planted in an intimate mixture with other species.
Clones of DED resistant elms such as Sapporo Autumn Gold or Belgica are grown in British tree nurseries and planted as large standard trees in parks and gardens but are far too expensive to plant in the wider countryside.