Ash (Fraxinus excelsior L.) is a highly valued timber and wildlife tree. It is a fast growing species, associated with several forest types. It has a broad distribution throughout Europe and occurs in widely different climates of both maritime and continental influence. It occupies large areas, owing to its presence in both the early and the mature stages of succession. Shade tolerant when young, ash becomes a strong light demander at around seven to eight years old. It rarely forms stands of any great extent, occurring more commonly as a component of mixed broadleaved woodland. Its drought tolerance and frost sensitivity make ash a species likely to be favoured in the short term by climate change, and indeed until recently had been expanding in range in Europe. Ash health and survival is currently seriously compromised by ash dieback caused by the fungus Hymenoscyphus fraxineus .