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The majestic elm is one of the most beloved of all our trees. Dutch elm disease has taken its toll and sadly the elm is disappearing from our landscape. Elm trees first made an appearance in the Miocene period, about 40 million years ago. Originating in central Asia, the tree has flourished and has established itself over most of North America, Europe and Asia. U. procera and U. glabra are both Native to Britain, while U. x hollandica was introduced by the Anglo-Saxons. Elms are deciduous and semi-deciduous trees comprising the genus Ulmus, family Ulmaceae, found throughout the Northern Hemisphere from Siberia to Indonesia, Mexico to Japan. The other genera in the Ulmaceae are Zelkova (Zelkova) and Planera (Water-elm). Celtis (Hackberry or Nettle Tree), formerly included in Ulmaceae, is now
English Elm - Ulmus procera
Found all over England in roadsides, hedges, margins of woods, but less common in the north. Frequently cultivated in west and south Europe. English Elm is (or was before the advent of Dutch Elm disease) the classic hedgerow tree of the English lowlands, suckering vigorously to produce long lines of characteristic compact crowns. It is best distinguished by its small, rounded, rough-surfaced, dark green leaves, which are longer on one side at the base, but rounded where they join the stalk. It has dark, finely ridged bark and slim, hairy twigs. Red flowers are produced in February or March, ripening by May, after the leaves have expanded, to give fruits with the seed nearer the top of the round wing. A variable tree with distinct local types maintained by vegetative propagation (suckering). Probably native, but its distribution and origin are imperfectly understood.
Small-leaved Elm U. minor typically has narrower leaves, with the unequal base joining the stalk at right-angles, and oval fruit-wings. It is an exceptionally variable tree, reproducing by suckers to give distinctive local types such as Cornish, Wheatley, and Plot Elms. Common in Europe, and probably introduced in Britain, it is now much reduced by disease. from the Collins Gem Guide to Trees (p.134)
Wych Elm - Ulmus glabra
The most easily recognized elm, Wych Elm is distinguished by its large, short-stalked leaves, and the absence of sucker shoots. The trunk often forks near the ground and the bark is smooth at first but later develops thick, straight ribs and turns grey. The leaves vary greatly in shape but are large and very rough to the touch. As in all elms, the base of the leaf extends further down the stalk on one side than the other, but in Wych Elm the long side crosses over the short stalk and hides it. The red flowers appear in late February and the winged fruits, with the seed set centrally, are visible before the leaves are expanded. Wych Elm is a common woodland tree, particularly in the north and west, and has shown considerable resistance to Dutch Elm disease. Wych derives from an old word for supple, referring to the twigs.
Dutch Elm U. x hollandica is thought to be a hybrid with U. minor. Once common, but heavily reduced by Dutch Elm disease, it has cracked bark, many suckers and spreading branches. Huntingdon Elm var. vegeta has straighter branches but both have longer-stalked, smoother leaves than Wych Elm, and seeds not in the middle of the fruit.
They have alternate, simple, single- or doubly-serrate leaves, usually asymmetric at the base and acuminate at the apex. The leaves are 6-9 cm long with a rough upper surface, and hairy underside. Elms are hermaphroditic, having perfect flowers, and which, being wind-pollinated, are without petals. The fruit is a round samara.
Elms, like other shade trees, are nature’s air conditioners. They help to cool not just by providing shade but by the transpiration of water from their leaves. In fact, the cooling effect of one urban elm tree is equivalent to five air conditioning units. And like all trees, elms are a natural air purifier converting carbon dioxide into oxygen. All species are tolerant of a wide range of soils and pH levels but, with one exception (European White Elm U. laevis), demand good drainage.
Selected for their shade cover, genetic variation was reduced making the species especially vulnerable to Dutch elm disease. After the disease reached Britain in 1967, more than 12 million English elms perished. Mature English elms can grow to 36m and have narrow crowns. Owing to the devastation caused by Dutch elm disease, to which all American and European species are susceptible, much effort has been made on both sides of the Atlantic to raise disease-resistant hybrids and cultivars, with the result that the number of named trees now exceeds 200. The English elm Ulmus procera Salis. was
Understanding how an elm tree lives and breathes is important in understanding how Dutch elm disease has spread. Just like the human cardio-vascular system of arteries and veins, a tree has a vascular system of long thin vertical tubes. This vascular system takes the water and nutrients from the roots and distributes them throughout the tree. In an elm, the cells that produce the vascular tubes are found just beneath the bark in a layer called the cambium. After each growing season, the inner part of the cambium dies. A new cambium is formed the next spring. If you cut through a tree trunk, you can see the tree rings. Each ring is a cambium layer. An elm tree has a very efficient vascular system but that also makes it vulnerable. The same qualities that allow the elm to efficiently draw water to its upper leaves also give fungi and insects easy access to the inner workings of the tree. The fungus that causes Dutch elm disease, for example, essentially clogs the elm tree’s vascular system. Dutch elm disease can be treated. However, because the tree’s vascular system is renewed every year, treatments have to be repeated annually.
Elm trees have entered our mythology - a mark of their prominence in the lives of early civilizations. Germanic tribes included the elm in their creation myth. Germanic Creation Myth The ancient Germanic peoples who came to inhabit much of Europe, believed that three gods, Odin, Vili and Ve, created the world. According to the myth, these three gods were walking by the sea examining their handiwork when they came upon two fallen trees. One was an ash, the other an elm. Odin imbued them with the spark of life. Vili endowed them with spirit and a thirst for knowledge. Ve gave them the gift of five senses. When they had finished, the fallen trees resembled the gods themselves. Out of the ash came man. Woman was created from the elm and her name was Embla.
Romans used living elms to support their grapevines - a practice called "marrying the vine to the elm." They also selectively bred elms producing many of the species we see today throughout their former Empire.
Cultivation and uses
Elm wood was valued for its interlocking grain, and consequent resistance to splitting, with significant uses in wheels, chair seats and coffins. The wood is also resistant to decay when permanently wet, and hollowed trunks were widely used as water pipes during the mediaeval period in Europe. Elms also have a long history of cultivation for fodder, with the leafy branches cut for livestock. The bark, cut into strips and boiled, sustained much of the rural population of Norway during the famine in the mid-19th century. From the 18th century to the early 20th century, elms were among the most widely planted ornamental tree in both Europe and North America. They were particularly popular as a street tree in avenue plantings in towns and cities, creating high-tunnelled effects. It had unique properties that made it ideal for such use: rapid growth, adaptation to a broad range of climates and soils, strong wood, resistant to wind damage, and vase-like growth habit requiring minimal pruning. In Europe, the Wych Elm U. glabra and the Smooth-leaved Elm U. minor var. minor were the most widely planted in the countryside, with the former in northern areas (Scandinavia, northern Britain), and the latter further south. The hybrid between these two, Dutch Elm U. × hollandica, occurs naturally and was also commonly planted. In parks and gardens, from about 1850 to 1920, the most prized small specimen elm was the Camperdown Elm, a contorted weeping cultivar of the Wych Elm Ulmus glabra Camperdownii, grafted on a standard Wych Elm trunk to give a wide, spreading and weeping fountain shape in large garden spaces. In Australia large numbers of English Elms U. procera were planted as ornamentals in the early 20th century.
Feeding and other inter-species relationships associated with Ulmus procera:
Elms in Worcestershire
There are three species of elm and several interspecific hybrid combinations that are either native or naturalised in Worcestershire. English Elm Ulmus procera is by far the most widespread of the three species. In spite of the ravages of Dutch Elm Disease it is probably found within most 1x1 km squares in the county. Its characteristics are that mature trees have a massive straight trunk persisting half way through the crown, the bark is deeply cracked which in maturity form square plates, there are branches at all levels which twist and ascend at the top of a dense domed crown, lower limbs become rapidly diffuse becoming short and slender. In sub-mature trees the majority of branches are ascending. The leaves are 5-9cm in length, ovate to circular with a short pointed apex; they are harshly roughened above and rough on the underside, when fully developed they are unusually curled or puckered (Mitchell 1994). The leaves are nearly always attacked by the elm leaf-gall mite Eriophytes ulmicola (Rackham 1980). The reasons for English Elm's U. procera continued widespread distribution is that it is native to our region and was widely planted right throughout the medieval period through to the 20th century, mainly in hedgerows (Rackham 1994). Although all mature English Elm trees have succumbed to the disease it survives in hedgerows because of its ability to produce vegetative suckers. Indeed it has largely abandoned sex as a means of reproduction. Its success is further enhanced by the fact that it is invasive and over time out-competes neighbouring species - hence where English Elm U. procera is present we get dominant stretches of elm hedges and dominant stands of suckering elm in woodland (Peterken 1981), often with no other shrub species present. Rackham (1994) considers that its ability to sucker profusely may have developed over time in response to the disease which has struck in past centuries.
Wych Elm Ulmus glabra Hudson (syn. Ulmus montana Loudon.)
Wych Elm Ulmus glabra is a broad spreading tree, the trunk usually forks into a Y shape. Sub-mature trees have smooth (hence 'glabra') silvery-grey bark which latter become fissured. The leaves are greater than 7cm in length; they are typically very rough on the upperside with more than 12 lateral veins covered in stiff white hairs, it has a short hairy petiole 2-5mm long, the leaves commonly have a three point apex; although this is not a diagnostic characteristic. It does not sucker freely, although it does coppice well (unlike English Elm U. procera). Wych Elm produces a mass of viable seed with relatively young trees reach fruiting maturity. Although it is vulnerable to Dutch Elm Disease senescence tends to occurs at a latter stage than English Elm U. procera. It is probably present in every 10x10 km square in the county. Wych Elm U. glabra is more tolerant of shady conditions and well adapted to northern climes where it is a major native component species of lowland mixed broad-leaved woodlands with Dog's Mercury (NVC W8) and lowland mixed broad-leaved woodlands with Bluebell (NVC WIO) in north-west England (Rodwell 1991). In Worcestershire it is an occasional component of such woods. It is often encountered in hedgerows, presumably because it was much planted.
Small-leaved Elm Ulmus minor Miller (syn. Smooth-leaved Elm
Ulmus carpinifolia G. Sucklow and Ulmus nitens Moench) Our rarest elm is the Small-leaved Elm Ulmus minor. Typically a tall tree with a narrow domed crown. Limbs in the upper crown are nearly all vertical, various size of branches ascend from the trunk, and unlike English Elm U. procera arch over to end in long pendulous branchlets with a narrow system of fine curled shoots. The bark has deep long, vertical fissures, commonly the branches have thick corky ridges. It has much smaller leaves than its counterparts being less than 7cm in length; although the leaf shape is extremely variable, they are most typically elliptic with the upper surface of the leaf being smooth and shiny green (Mitchell 1994). Where Small-leaved Elm U. minor is present it too is clonal i.e. produces suckers freely which are genetically identical to the parent plant. It is rarely attacked by the elm leaf-gall mite. The status of Small-leaved Elm U minor within the county is so far undetermined. Its main centre of distribution is in the east of England which is why it is also referred to as East Anglian Elm. Small-leaved Elm U. minor is probably not native to Worcestershire with its presence being due to deliberate introduction. It is scattered along a 5 kilometre stretch of the A449 between Crossway Green and Ombersley.
Elm hybrids and immediate types
Unfortunately for those people studying elms (know as pteleologists!) there are a bewildering number of elm types. Rackham (1980) cites elms as being the most difficult critical genus in the British flora, Richens (1983) recognises 27 different forms in Essex alone. Intermediates between Wych Elm U. glabra and English Elm U. procera are uncommon and thought to be evolutionary i.e. without fixed characteristics (Rackham 1986). However, it is Small-leaved Elm U. minor which shows the greatest variation and it is this species which hybridises readily with other elms.
Hybrids and intermediate types in Worcestershire
Hybrid elms with fixed characteristic and other intermediate forms are uncommon in Worcestershire because of the scarcity of Small-leaved Elm U. minor. In places where Small-leaved Elm U. minor and English Elm U. procera are found growing in close proximity some suckers have characteristic common to both species. It is likely, as Rackham states, that such crosses are typically variable and can not be classified as true hybrids as they are probably still evolving. However, there are some elm hybrids in the county which show characteristics identical or very close to some of the forms presently described by Richens, Rackham and Mitchell. A very distinctive mature elm is present at Barnard's Green on the Guarlford Road, Malvern. Its growth form is identical to that of the Huntingdon Elm Ulmus x hollandica var. Vegeta (syn. Ulmus x vegeta), described by Mitchell 1994; as a tree with a regular tall domed crown with a straight clean bole. Its leaves are elliptic, long-acuminate, 10-13 x 8cm, doubly toothed with a petiole between 1-2cm. It was a tree that was very widely planted in the British Isles (Stace, 1991), however, only a few trees currently now survive (Mitchell 1994). The most likely candidate for a naturalised hybrid elm is the so called 'Lineage' Elm which is specifically a woodland elm (Rackham, 1980). It has an intermediate leaf shape between Small-leaved Elm U. minor and Wych Elm U. glabra, but unlike the more familiar hybrid Dutch Elm Ulmus x hollandica it is non-invasive and coppices well. Lineage Elms are often found in homogenous stands and were probably deliberately planted in most situations. This tree is known to occur in Tiddesley Wood where it is locally common and may be scattered in other ancient woodland sites in Worcestershire. Whilst in the Lineage Elm and in some of the other hybrid combinations, phenotypic features can be reasonable determined, their true parentage can probably only be resolved as and when chromosomal analysis is undertaken. (A phylogenetic reconstruction of the Ulmus genus based upon morphological and sequence data is being developed by Jayne Armstrong of the Division of Environmental and Evolutionary Biology at the University of Glasgow. This will provide a new taxonomic framework which could enable the comprehensive identification of hybrid elms and other forms within the county.}
Elm Trees and the Native Elm Programme
Elms grew taller than all other trees in the landscape with both English Elm U. procera and Small-leaved Elm U. minor regularly attaining heights of 120 feet (over 30 metres) or more. Elm wood is of medium weight and strength, but distorts easily and has to be seasoned carefully. Its timber was much valued in building construction and for use in furniture (Milner, 1992). Elm trees with circumferences of over 190cm are rare within the county. In 1996 a national survey was initiated by the Conservation Foundation with the aim of identifying elm trees which could be used for propagation of disease-resistant native stock. Small-leaved Elm U. minor is less susceptible to the disease than English Elm U. procera. In certain parts of Essex and Suffolk elm trees with circumferences of more than 150cm are still commonplace. Likewise some Wych Elms U. glabra reach full maturity and appear not to contract the disease. So how many fully grown elm trees remain in Worcestershire? The answer is we do not know because we have no recorded data. However, we know of the existence of several Wych Elms trees, other still await discovery. One Huntingdon Elm Ulmus x hollandica var. Vegeta is present at Barnard's Green - are there others in urban situations? Recently a mature specimen of what is probably Small-leaved Elm U. minor was seen in a hedge to the north of Bewdley.
If we can find and record where our Worcestershire elm trees are distributed we will be able to replace elm trees using seed or cuttings from Worcestershire stock. If you are interested please pick up a copy of the Elm Newsletter in March 1998 at the Worcestershire Biological Recorders meeting.
Checklist of UK Recorded Ulmaceae
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