If a disease like ash dieback affects a high proportion of the ash trees in a wild wood, it is unlikely that a casual observer would even notice. The rate at which resistant varieties of ash, or other species such as sycamore and cherry, would replace them would be much faster than the ten years or so that the disease is thought to take to kill a tree (in fact, ash dieback is not known to kill mature trees, so any sort of dramatic effect is very unlikely indeed).

The effect on ground flora and woodland animals is also likely to be negligible. Few species are dependent on ash for anything – mainly just other fungal diseases. If the proportion of ash in woodlands was to fall, the trees that would benefit, such as oak, may well have even higher ecological value (many hundreds of species are known to live on oaks).

Over the last 50 years the amount of ash, Fraxinus excelsior, in England and lowland parts of Wales and Scotland has increased greatly as a result of lower grazing pressure and the decline of elms.

Botanical Society of the British Isles – http://www.bsbi.org.uk/ash_dieback.html