Shapes trees make against the sky insinuate themselves into images we keep from childhood: jagged shadows of a back-garden sycamore, candled pyramid of the school's conker tree. To those I must add the elms that guarded the processionary lawns of my home town, lifting their furrowed limbs above Brighton's civic geraniums. I saw them in their ruin a couple of decades ago, and wished I hadn't.
Earlier casualties of Ophiostoma novoulmi, the Dutch elm fungus, still stood in the hedgerows, skeletal, bone-white. In their death, an iconic silhouette of the English country evening was lost - the one that took Matthew Arnold: "Up past the wood, to where the elm tree crowns/ The hill behind whose ridge the sunset flames".
These lines turned up last week in a letter from a Cavan reader. Having lost the wych elm at his own gate to the disease, he has been pleased to find a young tree surviving in the depths of his patch of old woodland, and already 10 metres high. Now he has found "a whole nursery of sapling elms", some, in their turn, bearing catkins. Is this revival happening everywhere, he wonders, and will it last?
To weigh the fortunes of a tree that most people have simply forgotten needs some botanical history. Ireland's native elm - the one that came marching north with the oak from Iberia some 9,000 years ago - is the wych elm, Ulmus glabra, (quickly told by the lopsided shape of the base of the leaf). It suffered great devastation in Europe in a spread of elm disease 5,200 years ago, accelerated by the clearances of Neolithic farmers. The surviving trees in Ireland were those pushed out to rocky hillsides.
In the wave of new Irish tree planting in the late 18th and early 19th centuries, hundreds of thousands of elms were planted in estate parkland and hedgerows (and along Dublin's canals, for future wooden waterpipes). Most of these new trees were the "English" elm, Ulmus procera, which, unlike the wych elm, spreads by throwing up suckers from its roots.
It is this species that is most prone to Dutch elm disease (so-called because of the nationality of the scientists who first identified the fungus). More than 90 per cent of the British elms died in the 1970s - an estimated 25 million trees. But the roots rarely died, and vigorous suckers have regrown, often reaching 6m five to six metres before attracting the bark-feeding beetles that carry the deadly spore-dust of Ophiostoma. After the die-back, another crop of suckers springs up, so that ever-expanding elm thickets have become quite common in much of lowland England.
In Ireland, too, the English elm lives on, in a similar cycle of reinfection from dead or dying trees. There are, according the Tree Council of Ireland, "plenty" of young trees of around two metres in girth. Many old ones still endure as ivied stumps along country roads, their wands of sucker growth lopped off by mechanical hedge-slashers. Stephen Alexander, of Teagasc at Kinsealy, saw the elms of his south Dublin neighbourhood dying one by one through the 1970s. He has been on the look-out ever since for mature English elms which went through DED and have survived (if you know of one, phone him at 01-8460644).
He knows just two - one in Carnshill, Skerries, and another beside the Lusk-Skerries road - and watches them apprehensively each spring for the first sad wilting of the upper leaves.
The wych elm, our native species, has shown good resistance, its trees are genetically individual, and - as the Cavan example shows - self-sown regeneration can be vigorous. It is found in a truly wild form in the Antrim and Derry glens, and some trees on the old lake scarp beside Lough Neagh are several hundred years old. But the real test of their immunity may yet be to come, as global warming helps to intensify the northern spread of elm bark beetles.
In the south, some wych elms are still dying of disease. But Stephen Alexander keeps an eye on two fine specimens in the village of Blessington, Co Wicklow, and the Tree Council of Ireland has measured three others north of Kilcock, Co Meath and another near Emo in Co Laois, which range in girth from 12 feet to 15 feet and qualify for the Council's register of notable trees. Even more remarkable, in its own way, must be "the most southerly tree in Ireland" - a wych elm on Cape Clear Island, regularly doused in salt spray and just over one metre in girth: a survivor in every sense.
The latest epidemic of DED reached Ireland and Britain from North America, where millions of elms have succumbed. Much of the effort to overcome the disease and replace its casualties has also come from across the Atlantic.
One step has been the development of resistant hybrids, some bred from Asian elms. One of these was Saporo Autumn Gold, a Siberian elm fertilised with Japanese pollen. Its use was promoted in Europe by Pitney Bowes, the US office-systems multinational. In Ireland, some 500 were planted between 1987 and 1997, mostly at schools but also at the National Botanic Gardens and Mount Congreve.
In the US, surviving elms - especially in suburbs and city parks - have been regularly injected with fungicides, a costly and laborious process. Far more exciting is a new experimental preventative treatment based on research at the Forestry Faculty of the University of Toronto.
Not a fungicide or synthetic chemical, it works by stimulating the tree's own defences. A protein derived from a benign strain of the disease is injected to activate and boost the immune defence system, rather in the manner of a human vaccine. This has now been commercialised as "Elmguard": you can read more about it at the website of its developer, Dr Martin Hubbes, at: www. elmguard.com/message.htm
