New Study Reveals British Ash Trees Evolving Resistance to Dieback

Researchers at the Royal Botanic Gardens, Kew, and Queen Mary University of London have made a groundbreaking discovery regarding British ash trees, revealing that a new generation is exhibiting greater resistance to ash dieback than older trees. This study, published in the prestigious journal *Science* on June 30, 2025, highlights the role of natural selection in the evolution of these trees, providing renewed hope for their future in the British landscape.

Ash dieback, caused by the fungus *Hymenoscyphus fraxineus*, was first identified in Britain in 2012 and has since devastated ash populations across the country. Predictions from the time of its arrival suggested that as much as 85% of the ash trees could be lost to the disease, with no trees displaying complete immunity. The urgency of the issue prompted an emergency meeting of the UK government’s COBRA committee to address the crisis.

In their recent study, researchers analyzed the genetic material of ash trees established before and after the arrival of the fungal pathogen. They observed notable shifts in the frequencies of DNA variants associated with tree health across thousands of genomic locations, indicating that the offspring produced in the wake of the disease outbreak are more resistant than their predecessors. This finding aligns with Darwinian evolutionary predictions, demonstrating natural selection's impact on the genetic diversity of the ash population.

Professor Richard Nichols, Professor of Evolutionary Genetics at Queen Mary University of London, remarked, "A tragedy for the trees has been a revelation for scientists: allowing us to show that thousands of genes are contributing to the ash trees’ fightback against the fungus. Our detection of so many small genetic effects was possible because of the exceptional combination of circumstances: the sudden arrival of such a severe disease and the hundreds of offspring produced by a mature tree."

Dr. Carey Metheringham, a PhD researcher involved in the study, emphasized the role of natural selection in improving the resilience of future ash tree generations. However, she cautioned that natural selection alone may not suffice to produce fully resistant trees. "The existing genetic variation in the ash population may be too low, and as the trees become scarcer, the rate of selection could slow. Human intervention, such as selective breeding and the protection of young trees from deer grazing, may be required to accelerate evolutionary change," Metheringham stated.

Professor Richard Buggs, Senior Research Leader for Plant Health and Adaptation at the Royal Botanic Gardens Kew, expressed optimism over the findings, stating, "We are so glad that these findings suggest that ash will not go the way of the elm in Britain. Elm trees have struggled to evolve to Dutch elm disease, but ash are showing a very different dynamic because they produce an abundance of seedlings upon which natural selection can act when they are still young. Through the death of millions of ash trees, a more resistant population of ash is appearing."

This research not only exemplifies natural selection at work but also provides a real-world case study of DNA-level evolution, as described by Charles Darwin. It serves as a hopeful indication that, despite the tragic loss of many trees, a new generation of ash trees may thrive in the face of adversity. The implications of these findings extend beyond the survival of a single species; they also underscore the importance of genetic diversity and adaptive capacity in the face of emerging diseases in forest ecosystems worldwide.

In summary, the evolving resistance of ash trees to ash dieback presents a compelling case for the resilience of nature and the potential for recovery through natural processes. Future research and conservation efforts will be crucial in supporting this transition and ensuring the longevity of ash trees in Britain’s woodlands. The study by Metheringham et al. is a significant contribution to our understanding of plant evolution and disease resistance, with potential lessons applicable to other species facing similar threats to their survival.