Ash dieback is decimating ash trees Fraxinus excelsior across Europe. It is caused by Hymenoscyphus fraxineus, a fungus native to eastern Asia. This spreads into the shoots and eventually the trunk, leading to the death of the tree. However, the level of tolerance varies among individual trees. Trees with a low level of tolerance succumb quickly, whereas others can survive longer.
A recent study gives hope. In woodlands, the lowest levels of mortality are found in sites with the longest exposure to ash dieback, suggesting that resistant strains of ash may be occurring already.
