| Ulmus glabra | |
|---|---|
| Wych elm | |
| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Magnoliophyta |
| Class: | Magnoliopsida |
| Order: | Rosales |
| Family: | Ulmaceae |
| Genus: | Ulmus |
| Species: | U. glabra |
| Binomial name | |
| Ulmus glabra Huds. |
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| Synonyms | |
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Ulmus glabra, the Wych elm or Scots elm, has the widest range of the European elm species, from Ireland eastwards to the Urals, and from the Arctic Circle south to the mountains of the Peloponnese in Greece; it is also found in Iran. A large, deciduous tree, it is essentially a montane species, growing at elevations <1500 m, preferring sites with moist soils and high humidity.[1] The tree can form pure forests in Scandinavia, and occurs as far north as latitude 67°N at Beiarn in Norway. Wych elm has also been successfully introduced to Narsarsuaq, near the southern tip of Greenland (61°N).
The tree was by far the most common elm in the north and west of the British Isles,[2] and is now acknowledged as the only indisputably British native elm species. Closely related species, such as Bergmann's Elm U. bergmanniana and Manchurian Elm U. laciniata, native to northeast Asia, were once sometimes included in Ulmus glabra;[3] another close relative is the Himalayan or Kashmir Elm U. wallichiana.
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The word wych has its origins in Middle English wiche, from the Old English wice, meaning pliant or supple, and which also gives us wicker and weak. Owing to its former abundance in Scotland, it was occasionally known as the 'Scotch (sic) Elm', the name Loch Lomond, a corruption of the Gaelic Lac Leaman, or 'Lake of the Elms'.
Some botanists, notably Lindquist [4] [8] (1931) have proposed dividing the species into two subspecies:
However, there is much overlap between populations in these characters, and the distinction may be due to environmental influence, rather than genetic variation; the subspecies are not accepted by Flora Europaea.[5]
The Wych elm sometimes reaches heights of 40 m, typically with a broad crown where open-grown, supported by a short bole < 2 m. d.b.h. There are not normally root suckers; natural reproduction is by seed alone. The tree is notable for its very tough, supple young shoots, which are always without the corky ridges or 'wings' characteristic of many elms. The alternate leaves are deciduous, 6–17 cm long and 3–12 cm broad, usually obovate with an assymetric base, the lobe often completely covering the short petiole; the upper surface is rough. Leaves on juvenile shoots sometimes have three or more lobes near the apex.[6] The hermaphrodite flowers appear before the leaves in early spring, produced in clusters of 10-20; they are 4 mm across on 10 mm long stems and, being wind-pollinated, are apetalous. The fruit is a winged samara 20 mm long and 15 mm broad, with a single, round, 6 mm seed in the centre, maturing in late spring.[7][8]
While the species is highly susceptible to Dutch elm disease,[9][10] it is less favoured as a host by the elm bark beetles which act as vectors. Research in Spain has indicated the presence of a triterpene, alnulin, renders the tree bark less attractive to the beetle than the Field elm.[11] Moreover, once the tree is dying, its bark is quickly colonized by the fungus Phoma, which radically reduces the amount of bark available for the beetle to breed on.[12] The tree usually succumbs to disease a few years after achieving sexual maturity.
In 1998, over 700 healthy, mature trees were discovered on the upper slopes of Mount Šimonka in Slovakia, but it is now believed they had survived courtesy of their isolation from disease-carrying beetles rather than any innate resistance; 50 clones of these trees were presented to HRH The Prince of Wales for planting at his Highgrove Estate, and at Clapham, Yorkshire [9]. Indeed, DNA analysis by Cemagref in France has determined the genetic diversity within the species is very limited, making the chances of a resistant tree evolving rather remote. Nevertheless, the spread of Dutch elm disease to Scotland has revealed a number of Wych elms apparently surviving there unscathed, prompting the Royal Botanic Garden Edinburgh to clone the trees and inoculate them with the fungus to determine any innate resistance.
In trials conducted in Italy, the tree was found to have a slight to moderate susceptibility to elm yellows, and a high susceptibility to the elm leaf beetle Xanthogaleruca luteola [10].[13]
The Wych elm is moderately shade-tolerant, but requires deep, rich soils as typically found along river valleys.[14] However, the species is intolerant of flooding, as it is of prolonged drought.[15] Although rarely used as a street tree owing to its shape, it can be surprisingly tolerant of urban air pollution, constricted growing conditions and severe pollarding, as evidenced by the survival of those in Tsimiski Avenue in central Thessaloniki, Greece.[16]
As Wych elm does not sucker from the roots, and any seedlings are often consumed by uncontrolled deer populations, regeneration is very restricted, limited to sprouts from the stumps of young trees. The resultant decline has been extreme, and the Wych elm is now uncommon over much of its former range. It is best propagated from seed, although softwood cuttings taken in early June will root fairly reliably. Propagation from hardwood cuttings is notoriously difficult, even under mist conditions.
About 40 cultivars have been raised, although at least 30 are now probably lost to cultivation as a consequence of Dutch elm disease and/or other factors:
The tree has featured strongly in artificial hybridization experiments in Europe, notably at Wageningen in the Netherlands, and a number of hybrid cultivars have been commercially released since 1960.[17] The earlier trees were raised in response to the initial Dutch elm disease pandemic that afflicted Europe after the First World War, and were to prove vulnerable to the much more virulent strain of the disease that arrived in the late 1960s. However, further research eventually produced several trees effectively immune to disease, which were released after 1989.[18]
Too numerous to list
Only as cultivar 'Camperdownii' (Camperdown elm)
Widely available - in the UK, nurseries stocking this tree can be found by using the plantfinder function of the Royal Horticultural Society's website. [14] This tree is also stocked by many local nurseries and by the British Trust for Conservation Volunteers. [15]
The UK Champion listed in The Tree Register of the British Isles (TROBI) is at Brahan in the Scottish Highlands; it has a girth of 703 cm (2.23 m d.b.h.) and a height of 24 m [16]. Outside the Brighton area, among the rare survivors in the south of England (2010) is a mature tree at the University College sports ground, Abingdon Road, Oxford. Notable specimens in Edinburgh are to be found (2010) in Moray Place, Learmonth Gardens, Queen Street Gardens and The Meadows area.[19]