The next time you drive or walk down a country road, you may well notice that something is not quite right. Look around and you might see that tall ash trees in the verge-side hedgerows are no longer as handsome, their leaves sparse and scattered, even brown and wilting, while naked branches point accusingly to the sky. A disaster is unfolding, which, on the face of it, seems hardly less serious than the one that hit the countryside in the early 1970s, after ‘Dutch’ elm disease was imported in timber from Canada and killed 30 million trees. This time, the victim is the European ash (Fraxinus excelsior).
The disaster is plain, even to urban dwellers. The sound of chainsaws and tree shears is loud in the land
Hymenoscyphus fraxineus is a fungus indigenous to Asia, where ash species tolerate it, because pathogen and trees have evolved together. The fungus arrived in Europe 30 years ago. Thanks to failures in biosecurity, it then crossed the Channel, possibly as early as 2006, but certainly in 2012, in a consignment of young infected plants. The fungus produces spores, released in summer and borne on the wind that cause a disease called Chalara ash dieback. This results in crown decline, root collar necrosis and, eventually, death – which is often accelerated by secondary pathogens such as honey fungus and bracket fungus.
When the news of the disease broke in 2012, it prompted a general horrified fascination. But as time went on, the threat to ash trees became background noise, easy to ignore. No longer. The disaster is plain, even to urban dwellers, since ash trees grow in city parks and suburban streets as well as country hedgerows. The sound of chainsaws and tree shears is loud in the land.
The ash is a broad-leaved hardwood, with a smooth grey trunk that fissures with age. It has unique velvet-black leaf buds, followed by long, green, compound leaves. These flush later in the spring compared with other native deciduous trees, which means that a rich flora can develop at ground level in woodland. Male and female flowers are usually borne on separate trees, and the wind disperses the pollen; in late summer, distinctive hanging clusters of brown seed ‘keys’ appear. The leaves often drop in a heap after a frosty night.
The ash is a genuinely native British tree (unlike the elm), with a range that extends right through England and Wales and up into Scotland, especially on alkaline soils overlying limestone. Ash are vital denizens of woodland ecosystems, for the leaf litter has a high nutrient content and decays rapidly, which hugely benefits soil fungi and invertebrates. Ash woodland flora is richly diverse and five rare species, including the oxlip, are particularly associated with it. Like all large trees, ash filter out pollution, mitigate storm run-off and store carbon.
The timber, provided it is not affected by disease (which turns the wood from white to brown), is used for flooring, tool handles, oars, Irish hurling sticks and Morgan car frames – because of its remarkable capacity to absorb shocks. Ash also makes the best firewood, which is perhaps just as well, since there will be plenty of that about, as landowners rescue something of value from their stricken woods. Lady Celia Congreve’s poem from 1930 on the various woods for burning put ash first: ‘ash wet or ash dry/ a king shall warm his slippers by.’
In the past, ash foliage was used as forage for livestock in hungry winters, so trees were part of ancient ‘wood pasture’. Ash’s tolerance for being coppiced or pollarded means there are some very old trees about. (Coppicing is the process of cutting trunks almost to ground level, creating ‘stools’, while pollarding is cutting the crown right back.) In times past, my husband and I delighted in seeing the ash stools growing by the side of a country lane near Loweswater in the Lake District. We guessed they were a couple of centuries old, so broad and almost hollow were the boles, but still supporting strong, straight young poles. Delight turned to dismay when – years before ash dieback arrived – we came across men grubbing them up. Heaven knows why.
Thirty years ago, we planted hundreds of 18-inch ‘whips’ of a mix of native tree species in an acre of paddock beyond our garden. Previously, this had contained a single centenarian, hollow-centred ash, the haunt of tawny owls and woodpeckers. Our tiny ‘wood’, with the birds and insects it attracts, has become as dear to us as anything we possess. It contains 47 ash trees, a dozen of which we cut down to stumps when they started to encroach on their neighbours. We used the timber as firewood.
Mature trees take longer to decline, but most will go in the end, even if it takes a decade or two
It is the young growths from the stools that have succumbed quickest to ash dieback. Removing the infected stools won’t make any difference, since the fungal spores can be carried miles on the wind, so the rest will simply become infected from elsewhere. Mature trees take longer to decline, but most will go in the end, even if it takes a decade or two. Every day, I anxiously scan the crowns of 50ft ash trees, looking for signs of thinning at the extremities.
If these trees are dear to us, how much more must they be to the 30 invertebrates, four lichens and 11 fungi that are ash ‘obligates’, i.e. only found on ash. In all, 955 species benefit in some way from association with ash.
In 2019, an Oxford University study estimated that the cost of ash dieback, in lost benefits and the removal of dead and dying trees, would be £14.8 billion over the next 100 years – but with more than half of that, £7.6 billion, by 2030. What else can we expect when great tracts of countryside, many of them places of special aesthetic or scientific value, are affected? I might add that there are no grants available to private landowners for cutting down ash trees. Yet many grow in field hedgerows, next to roads or footpaths; these risk becoming unsafe when dead or dying, creating one more damn thing for hard-pressed farmers to deal with. We can safely leave some of our trees to stand, but those close to our neighbours’ boundaries may have to be felled – at substantial cost.
The Oxford report estimated that councils in Devon, a county badly hit, may incur annual costs of more than £30 million just to clean up dangerous roadside trees. In the Peak District, ash comprises 80 per cent of woodland and an even greater percentage in the steep ravines, a Special Area of Conservation. Here there is good news. Thanks to a diverse partnership, led by Natural England, the ravines are being replanted with ecologically similar large- and small-leaved limes, and wych elm. But it is arduous and skilled work that must continue for years.
The reason almost the entire population of elms died in the 1970s was that the vast majority were genetically identical. Mirabile dictu, as the Romans would say, most elms in Great Britain were descended from a single clone, the Antinian elm, imported from Italy via Spain to be used to stake vines. Such a wipeout won’t happen to Fraxinus excelsior, thank heavens, for it is genetically more heterogeneous.
Dr Jo Clark, head of research at Future Trees Trust (a charity founded to improve the stock of hardwood trees), estimates that 1 per cent of ash trees, i.e. perhaps 1.5 million, have substantial tolerance for the disease and can either live with it or will regrow after infection. It is these trees that have been the focus of FTT’s research and propagation project, carried out in conjunction with Forest Research, RBG Kew and Fera, under the umbrella of the Living Ash Project, and funded for the past ten years, until this month, by Defra. The work has resulted in the establishment of a ‘National Archive of Tolerant Ash’, a collection of grafted plants – the foundation for producing resistant trees at scale in future years – assembled and cared for at a site in Hampshire, and soon one in Scotland as well. The hope is that Defra will wish to fund a seed production programme, to build on this success. Dr Clark believes that there is hope for ash in the future. It certainly looks like it, but the present still feels grim.
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