A remarkable story of natural resilience is unfolding in Britain’s woodlands. Scientists have discovered compelling evidence that ash trees are spontaneously developing resistance to the devastating fungal disease known as ash dieback. This finding offers a crucial glimmer of hope for the future of a cherished species predicted to suffer catastrophic losses across the landscape.
The disease, caused by the fungus Hymenoscyphus fraxineus, arrived in the UK in 2012. Since then, it has killed millions of ash trees and significantly altered the appearance of affected woodlands. Experts previously estimated that up to 85% of Britain’s ash trees could be wiped out, a stark forecast prompting even high-level government meetings like COBRA to address the crisis.
However, a new study offers a more optimistic outlook. Researchers from the Royal Botanic Gardens at Kew and Queen Mary University of London (QMUL) have found that a younger generation of ash trees, growing naturally in the wild, is showing greater resistance to the disease compared to older trees. This suggests a powerful evolutionary process is actively at work.
Natural Selection Drives Resistance in UK Ash
The study provides strong support for Charles Darwin’s theory of natural selection. Scientists found that this evolutionary force is acting on thousands of locations within the ash tree’s DNA. This process is driving the development of resistance particularly in young trees as they emerge through the leaf litter where the Hymenoscyphus fraxineus fungus thrives.
Researchers compared the genetic makeup of ash trees established before the fungus arrived in Britain with those that grew afterwards. They observed subtle but significant shifts in the frequencies of DNA variants. These variants are associated with tree health and disease resistance. The shifts were detected across thousands of points in the trees’ genome. This indicated that the younger generation of ash trees possessed enhanced natural resistance to the fungus.
This finding is scientifically significant. It provides a clear, real-world example of how complex traits can evolve. Evolutionary change isn’t always driven by just one or two major genetic shifts. It can also result from many small changes happening simultaneously across numerous genes.
A Revelation for Scientists Amidst the Tragedy
Professor Richard Nichols, an evolutionary geneticist at QMUL, described the situation as a “revelation for scientists,” despite the tragedy for the trees. The arrival of such a severe disease created unique circumstances. Coupled with the high number of offspring produced by mature ash trees, scientists could observe this complex fightback at a genetic level. They saw that thousands of genes contribute to the ash trees’ resistance efforts.
Professor Richard Buggs, from both Kew and QMUL, highlighted a key difference between ash trees and elm trees. Elm trees were largely devastated by Dutch elm disease and struggled to evolve resistance quickly. In contrast, ash trees produce an abundance of seedlings. This creates a large population for natural selection to act upon effectively while the trees are still young.
Through the widespread death of millions of susceptible ash trees, a more resistant ash population is beginning to emerge. This natural filtering process is leaving behind trees with the genetic potential to survive and pass on resistance.
Study Details and Implications for Management
The groundbreaking study was published in the journal Science. It was largely funded by the Department for Environment Food and Rural Affairs (DEFRA). The research was conducted at Marden Park wood in Surrey. This woodland is managed by the Woodland Trust. It has been severely impacted by ash dieback.
Researchers like Dr. Carey Metheringham, a co-author from Kew and QMUL, expressed optimism. She stated that future generations should have a better chance against infection thanks to natural selection. However, she also added a note of caution. Natural selection alone might not be enough to create a fully resistant population quickly enough.
The existing genetic variation within the ash population might be too low. The rate of selection could slow as the overall number of ash trees decreases. This suggests that human intervention may be necessary to support and accelerate this natural evolutionary process.
Balancing Nature and Human Intervention
The findings have important implications for ash dieback management strategies. The authors suggest that afflicted trees shouldn’t always be cleared immediately. Leaving some diseased trees standing allows them to reproduce. They can then release their thousands of seeds. Removing all trees too soon could eliminate the chance for genetically resistant traits to be passed on to the next generation.
However, active human intervention is also seen as crucial. This includes selective breeding programs to identify and propagate the most resistant trees. Protecting young trees from other threats, such as grazing animals like deer, is also vital. Such measures can help tilt the odds in favour of the more resilient trees.
Rebecca Gosling from the Woodland Trust welcomed the research. She noted the devastating impact of introduced pathogens like ash dieback on native trees. She highlighted the importance of supporting natural regeneration in woodlands. Understanding how best to manage affected areas is key. This research helps inform those strategies.
Professor Nicola Spence, Chief Plant Health Officer at Defra, also acknowledged the study. She confirmed that tolerance to ash dieback is inheritable. She agreed that a combination of natural regeneration and breeding programs is essential. This combined approach offers the best path to securing the future of native ash trees in the UK.
Ash trees are a keystone species in British woodlands. They support over 1,000 associated species, including birds, mammals, and invertebrates. The potential loss of this species would drastically alter biodiversity and the British landscape. While the challenge remains significant, this evidence of natural evolution offers a vital path forward. It provides fresh motivation for conservation efforts. Protecting existing ash populations and allowing natural selection to proceed is crucial. Complementary human efforts can then build upon this natural resilience.
Frequently Asked Questions
How are British ash trees evolving resistance to ash dieback?
British ash trees are evolving resistance through natural selection. The ash dieback fungus arrived in 2012 and killed millions of susceptible trees. This left behind individuals with some natural genetic variation conferring better resistance. These surviving trees reproduce, passing on their advantageous genes. Scientists found this selection process is acting on thousands of DNA locations. Younger generations are showing greater resistance than older ones, proving evolution is happening naturally in the woodlands.
Where was the study on ash tree resistance conducted and by whom?
The main study highlighting this evolving resistance was conducted at Marden Park woodland in Surrey, UK. This site is managed by the Woodland Trust and has been heavily affected by ash dieback. The research was carried out by scientists from the Royal Botanic Gardens at Kew and Queen Mary University of London (QMUL). It was largely funded by the UK’s Environment Department (DEFRA) and published in the journal Science.
What does this discovery mean for managing ash dieback and conserving ash trees?
The findings offer hope but also guide management. Scientists suggest leaving some diseased trees to reproduce so resistant genes can spread naturally through seeds. However, natural selection alone may not be fast or strong enough. Therefore, conservation strategies should combine natural regeneration with human interventions. These include selective breeding programs to multiply the most resistant trees and protecting young seedlings from threats like deer grazing to give them the best chance of survival and growth.
The evidence of natural resistance in British ash trees provides a scientific basis for optimism. It underscores the power of evolution in combating disease and highlights the importance of long-term, integrated strategies combining natural processes with targeted human intervention to safeguard the future of this vital species and the biodiversity it supports.
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