Ash dieback, a devastating disease, has been responsible for destroying vast numbers of ash trees in continental Europe and Scandinavia since 1992. Caused by a fungus, three names have been in use for causal agent of this disease, initially Chalara fraxinea, then Hymenoscyphus pseudoalbidus, but the name Hymenoscyphus fraxineus is now being used widely.
The disease was first identified in the UK in 2012. Since then it has been found at hundreds of sites throughout Britain and Ireland although well over half of the findings have been associated with trees planted over the last 5-6 years, suggesting that plant trade has aided the arrival of this disease.
It is likely that resistance to ash dieback will evolve in the UK ash population over time through natural selection. This poses an important challenge for forest scientists: how to understand and accelerate this process so that the UK’s ash population can recover much more rapidly.