Ash dieback is a disease that is especially deadly to Britain’s native ash trees, Fraxinus excelsior.
It can kill young or coppiced ash trees in a single season. It is caused by a fungus, Hymenoscyphus fraxineus, another invasive alien species; this one seems to have come originally from eastern Asia. It was detected in Poland in the 1990s and has spread westwards through Europe since. It was first identified in Britain in 2012, in imported nursery stock saplings, but the following year was identified in the wider environment.
Although the fungus produces wind-borne spores, the spread of the disease in the park is probably the result of planting infected nursery stock over the years. We have had to fell young trees recently in an attempt to save our few mature ash trees. Fortunately most of the ash saplings were part of mixed plantations so they were felled in the normal process of thinning the plantations to allow healthier trees more space to grow.
Mature trees can survive the yearly cycle of ash dieback for a long time; an infected mature tree continues to support woodland species of birds, invertebrates and fungi. There are a number of invertebrates, lichens and mosses that depend wholly on ash trees. The dead wood is particularly important habitat and we would only remove it if it is considered to be a danger to park users.
habitat and food for a range of dependent species
Ash is an important native tree species; it can grow in all kinds of soils and conditions and its foliage is open and airy allowing light to reach the woodland floor, creating a rare environment of dappled shade. Our newly thinned plantations of young trees will now lack that kind habitat.
As the infection spreads, it is hoped that a native common ash with an in-built resistance to the dieback fungus will emerge. It will take some time to build up a stock of resistant seed and saplings but it seems the only way forward through a fairly gloomy prognosis.