Ash dieback experts identify shoots of hope for Britain’s threatened trees

The UK is home to more than 100m mature ash trees, and every spring tells the same grim story: leaves emerge, wither and drop within weeks, as ash dieback disease tightens its grip.

Millions stand dead in woodlands and hedgerows across the British Isles, with an estimated 2bn seedlings and saplings at risk. Many experts have long feared the future of this cherished, ecologically important native tree hangs in the balance.

But the latest scientific evidence tells a different story. Research suggests many of Britain’s ash trees might be more resilient than initially believed – and emerging solutions could help protect them.

“A lot of trees are going to die,” said Dr Matt Combes, the tree epidemiologist at the University of Warwick and the lead author of a review article summarising various insights. “But ash dieback infection is not a death sentence.”

Since the fungus responsible for ash dieback, Hymenoscyphus fraxineus, was identified in 2006, it has been the subject of a concerted, international research effort. Combes’s co-author, Prof Lynne Boddy, a fungal ecologist at Cardiff University, shared his measured optimism. “It’s probably not as bad as we were led to believe,” she said.

Despite earlier predictions that up to 95% of UK’s ash trees would die, the latest Europe-wide data suggests average losses of 50% over the next 30 years, though some areas will be hit far harder.

Since its arrival in Britain in the early 2000s, ash dieback has spread to every corner of the British Isles. “It’s part of the landscape now, so it’s [a question of] how do we live with it?” Combes said.

Efforts to protect ash trees are advancing on three fronts, each offering potential solutions.

1. Breeding disease-tolerant ash trees
While no trees appear immune, some exhibit only mild symptoms due to genetic factors that help them tolerate the disease. Since 2013, the Living Ash Project has been identifying these resilient trees and propagating them in the National Archive of Tolerant Ash. This government-funded programme aims to produce genetically diverse, disease-tolerant trees to repopulate affected areas. It is also identifying genetic markers that can be used to spot resistant trees in natural habitats. Though crucial, this work is slow, prompting some researchers to seek faster solutions.

2. Manage woodlands to build resilience
A wide range of environmental factors can be decisive in an ash tree’s fate. Young trees generally fare worse than old; vigorous trees outperform stressed ones; and isolated trees often survive better than those in dense stands. Climate matters too – humid conditions accelerate the disease, while periods of intense summer heat can, surprisingly, help infected trees, by killing H. fraxineus.

These insights are informing woodland management strategies. Though thinning ash-dense woods can help, government guidelines and tree experts, including the Woodland Trust, advise against felling infected trees unless they present a direct safety threat.

This is important because it allows disease-tolerant trees to set seed and reproduce, vital for regenerating landscapes with young, hopefully resistant, ash. As a fast-growing pioneer species supporting at least a 1,000 other species, ash plays a crucial role in woodland succession. However, the success of this natural regeneration depends heavily on deer control. Rebecca Gosling, the Woodland Trust’s lead policy advocate on tree health and invasive species, emphasises that without coordinated, government-supported action on deer numbers, efforts to regenerate woodlands can “potentially just become a bit of a deer-feeding exercise”.

Even trees that succumb to the disease have an important ecological role. Dead and dying trees provide essential habitats for species from fungi and insects to bats, owls and woodpeckers. Boddy said: “Woodlands in Britain are very depleted in nutrients. We’ve pillaged them [for timber] for thousands of years.” In her view, the dead wood generated by ash dieback can begin the long process of repaying this nutrient debt and restoring biodiversity and resilience to Britain’s woods.

3. Advance microbiome-based solutions
Perhaps the most surprising new frontier involves the ash tree’s microbiome – the diverse communities of bacteria, fungi and other microbes that grow within and on them. Researchers in Germany and Poland have identified particular microbes that are specifically associated with disease-tolerant trees. Other studies have focused on viruses that infect the ash dieback fungus.

These discoveries are being investigated as possible treatments. Experiments in Germany show that inoculating ash seedlings with specific bacteria can reduce disease severity. Researchers are also exploring fungi-targeting viruses as biological control agents – similar to new treatments developed for Chestnut blight, which decimated US chestnut forests in the 20th century. “I do think things like that are going to be the way forwards,” said Combes, though he acknowledged the challenges of applying inoculants at scale in natural woodlands. The Woodland Trust also welcomes this research but emphasised that unintended consequences were less likely if treatments used microbes native to the target landscape.

The race to future-proof forests

As the climate and biodiversity crises intensify, trees in Britain face an increasing array of threats. Erratic weather patterns weaken their defences, while new pests and pathogens are simultaneously expanding their ranges. The emerald ash borer offers a sobering example. This beetle, which has killed millions of ash trees across North America, is advancing from Asia into eastern Europe. Its march could present the European ash trees, already battling H. fraxineus, with a potentially devastating double threat.

Combes, who is modelling how these two perils might interact, hopes ash dieback’s rapid spread will serve as a wake-up call. “We’ve always been on the back foot,” he said, noting that the fungus was only identified after it had reached Britain. But with the emerald ash borer and other emerging tree diseases, it is going to be vital to react sooner.

The Observatree citizen project is mobilising this effort, with 200 trained volunteers across the UK watching for the earliest signs of 23 significant tree pests and pathogens. The government-funded research agency Forest Research is also pioneering a range of surveillance techniques, including sniffer dogs trained to identify tree diseases.

Despite the challenges ahead, the rapid advances triggered by ash dieback in understanding tree genetics, environmental factors and protective microbes offer new tools for protecting Britain’s native trees. As Combes said: “If you think everything’s going to die, you can end up thinking what’s the point? But [thanks to scientific research] there are clear avenues and ways forward.”