Scientists at the Royal Botanic Gardens, Kew and Queen Mary University of London have made a groundbreaking discovery about ash trees in British woodland. Researchers found that younger ash trees growing naturally in woodland exhibit greater resistance to the ash dieback fungus than older trees. This evolution is driven by natural selection acting on thousands of locations within the ash tree DNA.
The study published in Science offers renewed hope for the future of ash trees in the British landscape. Ash dieback, caused by the fungus Hymenoscyphus fraxineus, arrived in Britain in 2012 and has since wreaked havoc on the countryside. The disease is expected to kill up to 85% of ash trees, with none displaying complete immunity.
However, this new study reveals that younger ash trees are becoming more resistant to the disease. Researchers compared the DNA of ash trees established before and after the fungal invasion and observed subtle shifts in the frequencies of DNA variants associated with tree health. These shifts indicate that the younger generation possesses greater resistance than their predecessors.
This research demonstrates natural selection in action, as theorized by Charles Darwin. It also shows that thousands of genes are contributing to the ash trees’ fightback against the fungus. The study provides a real-world example of how natural selection can drive evolutionary change in response to environmental pressures.
The researchers believe that human intervention, such as selective breeding and protection of young trees from deer grazing, may be required to accelerate evolutionary change. However, they also emphasize the importance of supporting natural regeneration in woodlands to further our understanding of how to best manage ash woodlands.
This study contributes significantly to our knowledge base by demonstrating that tolerance to ash dieback is heritable, highlighting the potential for breeding programs and natural regeneration to secure the future of native ash trees.
Source: https://phys.org/news/2025-06-british-ash-woodland-evolving-resistance.html