Elms in Worcestershire

By Will Watson

(On 1st October JJ Day, AW Reid, GH Green and W Watson toured a large part of Worcestershire to visit some of the more unusual elms known to the Worcestershire Flora Project. The tour was initiated by Will Watson who prepared to following notes to help with identification. Afterwards we were probably more confused than ever! Elms are a complex and difficult group and await DNA fingerprinting. However, we collected a good few small branches with leaves and GHG now has a bulky plant press made of 3x2 ft sheets of ply with these pressed between masses of newspaper. Despite the problems of identification we should be pleased to hear of any big elm trees which have escaped elm disease and which we may not know of. Ed).

English Elm Ulmus procera Salisbury (syn. Ulmus campestris Miller)

There are three confirmed species of elm and several interspecific hybrid combinations that 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 1 km2 in the county. It characteristic 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, 1974). The leaves are nearly always attacked by the leaf-gall mite Eriophytes ulmicola (Rackham, 1980).

The reasons for its continued widespread distribution are that 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 (Peterkin, 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 bark (hence ‘glabra’) 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 hairy petiole greater than 3mm, the leaves commonly have a three point apex; although this is not a diagnostic character. 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 found in every 10km 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 broadleaved woodlands with Dog’s Mercury (NVC W8) and lowland mixed broadleaved woodlands with Bluebell (NVC W10) in northwest 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. Ulmus nitens Moench)

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. There are several U. minor subspecies and varieties. The majority have glabrous leaves hence the synonym ‘Smooth-leaved Elm.’

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. Small-leaved Elm U. minor is probably not native to Worcestershire with its presence being due to deliberate introduction, but this process is likely to have occurred over thousands of years.

A fine mature tree is present outside Dowles House, Bewdley (SO 775.765) and suckers are scattered along the railway embankment at Fernhill Heath (SO 868.589).

Plot’s Elm Ulmus plotii Druce (syn. Lock’s Elm Ulmus minor var. lockii Richens)

A tall tree with a very scanty crown. The top 5-6 metres are very thin and more on the one side of the tree than the other. It has relatively few short, almost horizontal branches from which slender, pendulous branchlets hang.

The unique characteristic of Plot’s Elm is its ability to produce proliferating short shoots. The terminal bus of most elms fall off, Plot’s Elm keeps on growing, in many cases producing on average up to eight leaves, opposed to say five in other species. The leaves are small, on average 8 x 4cm and obovate. They appear smooth on both sides but are minutely scabrous above and maybe hairy below but with white tufts beneath the axils. Leaves are typically deeply and doubly toothed, although newer leaves may have less pronounced serrations. There are 7-10 pairs of lateral veins. The petiole is 3-6mm (Stace, 1991).

The main centre of distribution is in the Trent valley around Newark on Trent. In Worcestershire it has yet to be confirmed. Any specimens of U. minor should be assessed to see if they have U. plotii features.

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.

Hybrid elms with fixed characteristic 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.

Rough Narrow-leaved Elm Ulmus minor Ssp. minor. Biotype U. diversifolia

An intermediate type which occurs in several places in Worcestershire is the ‘Rough Narrow-leaved’ elm. Most appear to originate from trees planted alongside highways and maybe of continental origin. However, this biotype has been recorded from various parts of the Midlands and East Anglia by Dr. Ronald Melville who identified it as a distinct species (East Anglian Elm U. diversiflora). The leaves are more or less rough above and have a leathery texture with rather blunt regular serrations. The fine twigs branch at right angles (like Wych Elm). Suckers are common and the trunk is often divided. Ten percentage of its foliage is said to have symmetrical leaves. Many of our elms which have been planted along our highways and may originate from the continent appear to display many of the characteristics of this subspecies.

Lineage Elm (Rackham, 1980)

Lineage Elm 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. It is believed to be a hybrid between these two species, but could be a species in its own right. Whilst its phenotypic features are reasonable well established its true parentage can probably only be determined as and when chromosomal analysis is undertaken. 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.

Midland Elm Ulmus glabra x plotii = U. x elegantissima

It can be distinguished from Dutch Elms (U. minor x U. glabra) by its erect habit often with pendant branches. It has small leaves with blunt serrations. This hybrid was recorded by Melville across the Gladder Brook near Ribbesford Wood.

Wheatley or Jersey Elm Ulmus minor Ssp. Sarniensis (Stace) Ulmus sariensis (C.K. Schneid) Ulmus wheatleyi (Simon-Louis)

Conic crown, even and regular. Branches of all sizes from bole, densely ascending parallel at 45§ or more steeply, the angle decreasing towards the top where nearly vertical, progressively shorter towards the tree apex. Leaves are narrow elliptic to obovate, 7 x 4.5cm, shiny dark green, scarcely tufted in axils beneath. Bark has almost square plates as in U. procera, but still vertically fissured; large boles are fluted (Mitchell, 1974). Present as planted trees on southern verge to A44 at Norton juxta Kempsey close to Junction 7 on the M5.

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 Elm U. glabra reach full maturity and appear not to contract the disease.

So how many 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. Recently the mature specimen of Small-leaved Elm U. minor was recorded 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.

Bibliography

[ 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 should enable the identification of hybrid elms and other forms within the county.