Ash trees

 

The UK is home to over 100 million mature ash trees, yet each spring reveals a disheartening pattern: new leaves emerge, wither, and fall within weeks, as ash dieback disease tightens its grip. Millions of ash trees now stand dead across the British Isles, with an estimated 2 billion seedlings and saplings at risk. For years, experts feared this ecologically vital native species faced near extinction.

However, recent scientific findings offer a glimmer of hope, suggesting Britain’s ash trees may be more resilient than previously believed, and emerging solutions could help safeguard their future.

“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.”

Ash dieback, caused by the fungus Hymenoscyphus fraxineus, was first identified in 2006 and has since been the focus of intense international research. Prof. Lynne Boddy, a fungal ecologist at Cardiff University, and her colleagues are cautiously optimistic. “It’s probably not as bad as we were led to believe,” she said.

Initial predictions suggested up to 95% of the UK’s ash trees could perish. However, Europe-wide studies now indicate that average losses may be closer to 50% over the next three decades, though some areas will be far more severely affected.

Since its arrival in Britain in the early 2000s, ash dieback has spread throughout the British Isles. Efforts to combat its effects are progressing on three fronts: breeding disease-tolerant trees, improving woodland management, and exploring microbiome-based solutions. Each approach holds promise for mitigating the disease’s impact.

“It’s part of the landscape now, so it’s [a question of] how do we live with it?” Combes said.

Breeding Disease-Tolerant Ash Trees

While no ash trees appear completely immune to ash dieback, some exhibit mild symptoms due to genetic factors that enhance their tolerance. The Living Ash Project, established in 2013, is identifying and propagating these resilient trees through the National Archive of Tolerant Ash. This government-funded initiative aims to create genetically diverse, disease-tolerant ash populations capable of repopulating affected areas. Researchers are also identifying genetic markers to help locate resistant trees in natural habitats. However, breeding disease-tolerant trees is a slow process, prompting some scientists to seek faster alternatives.

Managing Woodlands for Resilience

Environmental factors play a critical role in determining whether ash trees succumb to or survive the disease. Younger trees are generally more vulnerable, while vigorous, well-maintained trees are more likely to withstand infection. Surprisingly, isolated trees often fare better than those in dense stands, and extreme summer heat can sometimes kill the fungus, offering a reprieve for infected trees.

These insights are shaping woodland management strategies. Experts, including the Woodland Trust, recommend against felling infected trees unless they pose safety risks. Allowing disease-tolerant trees to mature and set seed is vital for natural regeneration. However, the success of these efforts hinges on controlling deer populations, which can decimate young ash saplings. Rebecca Gosling, the Woodland Trust’s lead policy advocate, stresses the need for coordinated, government-backed action to manage deer numbers, warning that unregulated populations could render regeneration efforts futile.

Even trees that succumb to ash dieback contribute ecologically. Dead and dying ash trees provide habitats for a wide range of species, including fungi, insects, bats, owls, and woodpeckers. Prof. Boddy notes that Britain’s woodlands, depleted of nutrients after centuries of timber extraction, can benefit from the nutrient recycling that dead wood facilitates. This process could help restore biodiversity and resilience to the UK’s forests.

Advancing Microbiome-Based Solutions

A promising new frontier in combating ash dieback lies in understanding the tree’s microbiome—the community of microbes living on and within ash trees. Researchers in Germany and Poland have identified specific microbes associated with disease-tolerant trees. Some studies have also explored viruses that infect the ash dieback fungus.

Experiments show that inoculating ash seedlings with beneficial bacteria can reduce disease severity. Similarly, fungi-targeting viruses are being investigated as potential biological control agents, akin to treatments developed for Chestnut blight in the United States. While these approaches are still in their early stages, they hold significant potential. However, scaling such treatments for use in natural woodlands remains a major challenge. The Woodland Trust supports these efforts but cautions that treatments should use microbes native to the UK to avoid unintended ecological consequences.

Challenges Ahead

The twin crises of climate change and biodiversity loss are intensifying threats to Britain’s trees. Erratic weather patterns weaken tree defences, while new pests and pathogens are spreading. One particularly alarming threat is the emerald ash borer, a beetle that has decimated ash populations in North America and is advancing from Asia into Europe. For European ash trees already battling H. fraxineus, this could create a devastating double threat.

Dr. Combes, a researcher modelling the potential interaction between these threats, hopes the rapid spread of ash dieback will serve as a wake-up call. “We’ve always been on the back foot,” he notes, emphasising the need for proactive measures to address emerging tree diseases. The Observatree project, a citizen science initiative, is mobilising efforts to detect tree pests and pathogens early. Supported by 200 trained volunteers, it monitors 23 significant tree threats across the UK. Additionally, Forest Research, a government-funded agency, is pioneering innovative surveillance techniques, including the use of sniffer dogs to detect tree diseases.

A Resilient Future for Ash Trees?

Despite the challenges, advances in genetics, woodland management, and microbiome research provide new tools to protect Britain’s ash trees. These efforts underscore the importance of swift action and collaboration among researchers, policymakers, and the public. As threats to native trees grow, the lessons learned from ash dieback could prove invaluable in safeguarding the UK’s forests for generations to come.

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.”

 

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