An elegy for the ash tree

Fifty years after the English elm succumbed to Dutch elm disease, another of our cherished natives is disappearing, due to a fungus thought to have arrived in Britain in saplings imported from the Netherlands.

By Isabella Tree

An Ash tree (Fraxinus excelsior) in the Peak district, England. Situated on a steep hillside near Buxton, Debryshire. A dark and moody sky overhead.

A year after the first case of Chalara, or “ash dieback”, was reported in the south-east of England in 2012, we began to notice casualties at Knepp, our 3,500-acre rewilding project in West Sussex. It’s not uncommon to see dead standing trees here. The landscape, driven by free-roaming animals, is now a mosaic of wood pasture, thorny scrub and wetlands – the kind of unkempt forest King John might have been familiar with when he came here to hunt fallow deer and wild boar in the early 13th century. When we began rewilding 20 years ago, we vowed to leave as many dead trees – vital habitat for wildlife – as we could.

But in the past five years the death rate has grown disproportionately, as the skeletal limbs of ash begin to semaphore their distress. Ash is the UK’s second most abundant native tree after the oak and Knepp has every permutation: open-grown parkland trees 300 years old; ash folded into ancient hedgerows; commercial plantations from before the First World War. With its straight grain, ash is one of the toughest hardwoods: it is the shock-absorber, treasured for furniture, tool handles and oars. Tree stumps from Knepp’s ash plantations were once used for sticks for the Irish game of hurling, the “clash of the ash”. Ash was valued for fodder, too. On the banks of our green lanes (old droving roads from Sussex to London) candelabras of pollarded ash used to provide fresh leaves for cattle on the move – food, but also medication, a salve for muscular aches.

It seems unimaginable that, 50 years after the English elm succumbed to Dutch elm disease, another of our cherished natives should be disappearing. According to the Woodland Trust 80 per cent of the estimated 150-180 million ash trees across the UK will be lost. The culprit is an ash-specific fungus, Hymenoscyphus fraxineus, the fruiting bodies of which release thousands of wind-borne spores. The spores infect the leaves, producing dark lesions. Soon, diamond-shaped lesions appear on the trunk, and the tree either succumbs to the disease itself or to another that takes advantage of its compromised condition.

The ash fungus is thought to have arrived in Britain in February 2012 in a consignment of saplings imported by a nursery in Buckinghamshire from a commercial nursery in the Netherlands. Though we’ve known for decades the disease risk of importing tree stock to the UK, a large number of saplings still originate abroad. When we replanted an ancient hedgerow at Knepp, outside the rewilding project, we bought our ash saplings from the very nursery that, a year later, imported the disease.

The irony has not been lost on us. Our rewilding project was already demonstrating how readily trees grow on their own, if you just let them. In fact, wild trees have by far the best start in life. Thorny shrubs act as their nursery, receiving seeds blown by the wind or dispersed by birds, and providing shelter for the sapling as it grows. As well as affording protection from animals, shrubs and nearby plants provide vital nutrients to the sapling through subterranean root systems interlocked with mycorrhizal fungi: a life-support system nurseries simply cannot replicate.

Why did we instinctively reach for the credit card to buy saplings with an alien provenance? I can only explain it as cultural amnesia. The commercial plantation model has come to dominate our lives: we’ve forgotten we can grow trees without it.

It’s not just the financial or even the carbon cost of commercial nurseries (the intensive systems of propagation, imported peat soils, fungicides, herbicides, water, infrastructure, transportation) we should be resisting; it’s the genetic diversity and Darwinian “fitness” of the trees themselves.

When we plant commercially produced saplings, we’re planting stock derived, invariably, from a narrow, selective genetic resource, lacking site-specific adaptations. In the wild, trees have an astonishing ability to respond to change, both sudden and incremental. Because they regularly produce a vast number of seeds and each of these seeds is produced by pollen that has arrived from diverse sources, the genetic variation inherent in trees is enormous. The process of natural selection promotes the survival of individuals best suited to the local conditions, but the trees continue to adapt to new threats and conditions as they arise.

Expanding natural regeneration throughout the countryside – rewilding – is by far the best way of helping our native trees meet the challenges of climate change and increased frequency of droughts and extreme weather events. It is also their best chance of survival against disease.

Initially it was thought none of our common ash would survive in the UK and scientists were suggesting hybridisation with other exotic ash species to introduce resistance. However, we now know that almost every ash population in Britain contains significant numbers of resistant individuals. Some of our mature ash trees at Knepp are so far unaffected and may prove to be resistant. Trees can respond effectively to attack by pest or pathogen. As disease wipes out non-resistant individuals the survivors breed with each other, creating a new generation of disease-resistant trees. No method of seed collecting and propagation by human hand can come close to the inherent resilience of natural regeneration.

As we pray for our native-born ash survivors to pull off a miracle, to secure the future of their species over the next century, we can, at least, resist another compulsion – to put a chainsaw to the casualties. Where it’s safe to leave deadwood standing, in places where there is little risk to people, the ash, in its death throes, will provide life in abundance for others. At Knepp, wild bees have already colonised the hollow trunks. Owls and bats nest in the cavities, woodpeckers drill for deadwood insects and, on a summer’s evening, it’s not uncommon to see a turtle dove – one of our rarest birds – territorially crooning from a withered bough, the phoenix from the ashes.

Isabella Tree is the author of “Wilding: The Return of Nature to a British Farm” (Picador)