Elm

• 1. Introduction

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  Elm trees once lined nearly every great boulevard in the Western world. From the cathedral arches of American elm canopy along the National Mall in Washington to the densely hedged English countryside where elms grew in concentrations exceeding a thousand trees per square kilometre, this genus shaped what cities and villages looked like for centuries. Then, within a few decades, almost all of them died.

  The story of the elm is not simply the story of a tree. It is the story of an ecological catastrophe so thorough that it altered the appearance of entire nations, a political symbol carried into revolutions on three continents, a tree so woven into myth that the ancient Greeks named nymphs after it, and a subject of ongoing scientific effort to bring it back. How did one microfungus, dispersed by beetles, accomplish what centuries of neglect could not? And what exactly was lost when the great elms fell?

• 2. Anatomy of a Genus

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  Ulmus, the scientific name for elm, belongs to the family Ulmaceae and ranges across most of the Northern Hemisphere. Its reach extends from North America and Eurasia southward into Iran, Libya, and parts of Indonesia. Roughly thirty to forty species make up the genus, though pinning down the exact number has always been difficult.

  Oliver Rackham, who studied British flora closely, described Ulmus as the most critical genus in the entire British flora. He wrote that species and varieties are a distinction in the human mind rather than a measured degree of genetic variation. The ease with which elms hybridize blurs the lines between species, and some populations have developed into local microspecies that reproduce only vegetatively, producing no viable seed at all. Asia holds the greatest diversity, with approximately two dozen species; only three species are endemic to Europe and eight to North America.

  The tree's physical character is distinctive. Leaves are alternate and typically doubly serrated, asymmetric at the base, and tapering at the tip. The fruit is a samara, a winged seed, that is flushed with chlorophyll so it can photosynthesize before the leaves even emerge. British elm samarae are astonishingly light; around fifty thousand of them weigh a single pound. The American elm can grow to more than thirty metres in height, often with a forked trunk that creates the recognisable vase silhouette. In evolutionary terms, elms are distant relatives of cannabis, mulberries, figs, hops, and nettles, all belonging to the same urticalean rosid clade. The oldest fossils of the genus are leaves dating from the Paleocene, found across the Northern Hemisphere.

• 3. Dutch Elm Disease

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  In the 1920s, Dutch botanists Bea Schwarz and Christina Johanna Buisman first described a disease that was attacking elms across Europe and worked out its cause. The name "Dutch elm disease" stuck, not because the Netherlands was responsible for it, but because it was Dutch researchers who identified it.

  The disease is caused by a microfungus that two species of Scolytus bark beetles carry between trees. When the beetles feed or lay eggs beneath elm bark, fungal spores enter wounds in the tree and invade the xylem, the vascular system that carries water from roots to leaves. The tree responds by producing tyloses, structures that block the xylem in an attempt to contain the invasion, but in doing so the tree effectively starves itself of water.

  The first, less aggressive strain of the fungus, Ophiostoma ulmi, arrived in Europe from Asia in 1910 and was accidentally introduced to North America in 1928. Viruses in Europe gradually weakened it, and it had nearly disappeared by the 1940s. The damage it did in North America was more severe because the American elm, Ulmus americana, is more susceptible, and that very susceptibility masked the emergence of a second strain.

  Ophiostoma novo-ulmi appeared in the United States sometime in the 1940s, initially assumed to be a mutation of the first strain. It was three times more virulent. Britain first detected it in the early 1970s, traced to a cargo of Canadian rock elm brought in for the boatbuilding industry. It swept through western Europe rapidly, then in a parallel wave, a second subspecies, O. novo-ulmi subsp. novo-ulmi, devastated Eastern and Central Europe. The two subspecies eventually met and hybridized where their ranges overlapped.

  In France, researchers inoculated more than three hundred clones of European species and failed to find a single variety with any significant resistance. No sign has emerged that the current pandemic is waning, and the fungus has shown no susceptibility to the virus-like agents, called d-factors, that had eventually weakened the original O. ulmi. Australia escaped entirely, thanks to geographical isolation and strict quarantine; the provinces of Alberta and British Columbia in western Canada also remain unaffected.

• 4. The Golden Age of Elm

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  From the eighteenth century to the outbreak of the First World War, elms stood at the centre of horticultural fashion across Europe and North America. They were planted in avenues down city streets, their interlocking canopies creating what observers described as high-tunnelled effects. Their rapid growth, their tolerance of air pollution, and the comparatively quick decomposition of their fallen leaves in autumn all made them practical as well as beautiful.

  One of the earliest ornamental elms on record is the ball-headed graft narvan elm, Ulmus minor 'Umbraculifera', cultivated in Persia from time immemorial as a shade tree and planted across cities in south-west and central Asia. In England, the English elm came to dominate horticultural planting, most commonly in hedgerows, sometimes at densities exceeding a thousand trees per square kilometre. South-eastern Australia and New Zealand received large numbers of English and Dutch elms in the nineteenth century. In northern Japan, the Japanese elm was widely planted as a street tree.

  From roughly 1850 to 1920, the most prized small ornamental elm in parks and gardens was the 'Camperdown' cultivar, a contorted weeping form of the wych elm grafted onto a non-weeping trunk to create a wide, spreading, fountain shape. The 'weeping' cultivars 'Camperdown' and 'Horizontalis' were grafted at two to three metres, while the dwarf cultivars 'Nana' and 'Jacqueline Hillier' were grafted at ground level.

  The belle epoque, as some horticultural historians have called it, began to unravel with the First World War. The war's devastation fell particularly hard on Germany, the origin of at least forty elm cultivars. The demise in 1944 of the Spathe nursery in Berlin, a major source of elm propagation, accelerated the decline. When Ophiostoma novo-ulmi broke out in the late 1960s, the tree's fortunes reached what one account calls its nadir.

• 5. Revolution and the Liberty Elm

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  Long before Dutch elm disease, elms had already acquired a charged political meaning. The cutting of an elm near Gisors in Normandy in 1188 became a diplomatic altercation between the kings of France and England. From there, the tree's association with political upheaval deepened over the following centuries.

  In colonial Boston, an American white elm became the Liberty Tree. From 1765, the first resistance meetings against British taxation were held in front of it. When British forces felled it in 1775, knowing it was a symbol of rebellion, Americans responded by planting Liberty Elms widely and sewing elm symbols onto revolutionary flags. Elm planting by American presidents later became a tradition.

  In France, Les arbres de la liberte, Liberty Trees, were often elms. A priest in Vienne, Isere, inspired by the Boston elm, planted the first in 1790. In the French Republican Calendar, in use from 1792 to 1806, the twelfth day of the month Ventose, corresponding to the 2nd of March, was officially named jour de l'Orme, the Day of the Elm. Premier Lionel Jospin, bound by tradition to plant a tree at the Hotel Matignon, insisted on an elm, choosing the disease-resistant hybrid 'Clone 762', which he called the tree of the Left.

  After the Greek Revolution of 1821-32, a thousand young elms were brought from Missolonghi to Athens and planted in 1839-40 in the National Garden. In Montepaone, Calabria, an elm planted in 1799 to mark the founding of the Parthenopean Republic survived until a recent storm brought it down; it has since been cloned and replanted.

  The tree's political associations could be melancholy as well as triumphant. On the morning of his execution on the 30th of January 1649, King Charles I, walking to the scaffold at the Palace of Whitehall, turned to his guards and pointed out an elm near the entrance to Spring Gardens that his brother had planted in happier days. The tree was said to be still standing in the 1860s.

• 6. Elm in Myth and Literature

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  In Greek mythology, the nymph Ptelea, whose name simply means elm, was one of the eight hamadryads, the nymphs of the forest and daughters of Oxylos and Hamadryas. The poet Callimachus, writing in the third century BC, describes the infant goddess Artemis testing her silver bow by shooting first at an elm, then at an oak, before turning her aim on a wild animal.

  The earliest reference to elms in literature appears in the Iliad. When Achilles kills Eetion, father of Andromache, the mountain nymphs plant elms on his tomb. Later in the same poem, when the River Scamander overflows and threatens to drown Achilles, the hero grabs the branch of a great elm to save himself. The tomb of Protesilaus, the first Greek to fall in the Trojan War, was also covered with nymph-planted elms. According to legend, those elms grew to be the tallest in the known world, but whenever their topmost branches caught a glimpse of the ruins of Troy, they immediately withered, still carrying the hero's grief. The first-century AD poet Antiphilus of Byzantium recorded this story in the Palatine Anthology.

  In Virgil's Aeneid, a great shadowy elm stands at the entrance to the Underworld. Vain dreams, the poem says, are wont to roost in it under every leaf. Virgil also alludes to a Roman superstition that elms were trees of ill-omen because their fruit seemed valueless. Scholars have identified two recurring elm motifs in classical literature: the Paradisal Elm, rooted in pastoral idylls and the ancient image of elm and vine together, and the Elm and Death motif, traceable to Homer and Virgil.

  The elm-and-vine pairing runs deep. Ovid in his Amores characterizes the elm as loving the vine, and the ancients spoke of the marriage between elm and vine. In pastoral poetry, elms mark places of shade and peace; in the first Idyll of Theocritus in the third century BC, a goatherd invites a shepherd to sit beneath an elm and sing.

  In Germanic and Scandinavian mythology, the first woman, Embla, was fashioned from an elm. In Japanese mythology, the chief goddess of the Ainu people, Kamuy Fuchi, was born from an elm impregnated by the Possessor of the Heavens. Shakespeare placed an elm in A Midsummer Night's Dream, where Titania addresses Nick Bottom with an elm simile, casting the tree as a masculine figure entwined by ivy. In E. M. Forster's Howards End, one of the most famous kisses in English literature takes place beneath a great wych elm.

• 7. Wood, Food, and Medicine

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  Elm wood has an interlocking grain that resists splitting. Medieval craftsmen put this to work in wagon-wheel hubs, chair seats, and coffins. The bodies of Japanese Taiko drums are often cut from old elm trees precisely because that resistance to splitting makes it possible to nail the skins tightly; a set of three or more drums is often cut from the same tree.

  The wood also resists decay when permanently submerged. Hollowed elm trunks served as water pipes across medieval Europe, and elm timbers were used as piers in the construction of the original London Bridge. Long, straight elm trunks supplied timber for ship keels. Bowyers prized elm too; a large portion of the ancient bows found in Europe are elm, and during the Middle Ages, elm was used to make longbows when yew was unavailable.

  The first written records of elm appear in Linear B lists of military equipment from Knossos in the Mycenaean period. Some chariots listed there are of elm, and the lists mention elm wheels twice. Hesiod records that ploughs in ancient Greece were also partly made from the wood.

  Beyond timber, elms fed people directly. Elm bark cut into strips and boiled kept much of the rural population of Norway alive during the great famine of 1812. Elm seeds are exceptionally nutritious, containing forty-five percent crude protein and less than seven percent fibre by dry mass. The Romans and, more recently, Italian farmers planted elms in vineyards as living supports for grapevines, lopped at three metres, with the pruned branches used for fodder and firewood.

  The inner bark of the slippery elm, Ulmus rubra, has a long medicinal history as a demulcent, a substance that soothes mucous membranes, and the Food and Drug Administration has approved it for sale as a nutritional supplement in the United States. Elm also appears among the thirty-eight substances used to prepare Bach flower remedies.

• 8. The Road Back

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  Efforts to breed elms resistant to Dutch elm disease began in the Netherlands in 1928 and continued without interruption through the Second World War, ending only in 1992. Similar programmes started in North America in 1937, in Italy in 1978, and in Spain in 1986.

  In the United States, research at Michigan State University in East Lansing, funded by the National Park Service, explored genetic engineering techniques. In 1993, Mariam B. Sticklen and Mark G. Bolyard published results from that work. By 2007, researchers A. E. Newhouse and F. Schrodt at the State University of New York College of Environmental Science and Forestry in Syracuse reported that young transgenic American elms had shown reduced disease symptoms and normal mycorrhizal colonization.

  Meanwhile, conventional breeding produced results. Careful selection in North America yielded several cultivars resistant to DED, notably 'Valley Forge' and 'Jefferson'. In Spain, researchers discovered that the European white elm, Ulmus laevis, may owe its practical resistance not to antifungal genes but to a triterpene called alnulin, which makes its bark unattractive to the beetles that carry the fungus. Field elms highly resistant to DED have also been found in Spain and form the basis of a major breeding programme there.

  The market has been slow to follow the science. In the Netherlands, sales of elm cultivars fell from over fifty-six thousand in 1989 to just six thousand eight hundred in 2004. In the UK, only four of the new American and European releases were commercially available in 2008. Enthusiasm was dampened by earlier, supposedly disease-resistant Dutch trees released in the 1960s and 1970s that failed to perform. More than three hundred named cultivars now exist, though possibly more than one hundred twenty of the older clones have been lost to cultivation.

  The National Elm Trial in North America, begun in 2005, is assessing the nineteen leading cultivars raised in the United States over a ten-year period. The oldest American elms in Central Park, planted in the 1860s by Frederick Law Olmsted, still stand along the Mall and Literary Walk, forming a cathedral-like canopy four rows deep, maintained now with aggressive pruning and replanting of the resistant 'Princeton' and 'Valley Forge' cultivars.