Ash Dieback (Hymenoscyphus fraxineus)
This is a fungus disease, one of many diseases and pests of trees, which are generally considered a beneficial part of a natural ecosystem. For example, Oak trees are celebrated for supporting hundreds of pests and diseases - or fungi and invertebrates, as they could more positively be described.
So why is Ash Dieback dreaded and feared, if it is just one of thousands of species in our ecosystem? The reason it arouses such concern is that it is a recent arrival to Europe, having arrived in Poland in the 1990s (see Fraxback website). New or alien diseases sometimes cause devastation to forests, as with American Chestnut Blight in the early 20th century.
However, very few diseases do actually cause this much damage. Estimates of the number of ash trees to succumb to this disease vary widely, but between 5% and 25% of trees are thought to be resistant in Europe, and if this is so then woods are likely to recover naturally and rapidly.
Semi-natural woods in Shropshire tend to be highly diverse and are therefore resilient to change.
On the whole, Ash Dieback will probably in the end be a beneficial and stabilising influence on the ecosystem in Shropshire. Ash trees (Fraxinus excelsior) have increased hugely in number over the last 70 years or so and are abundant throughout the county. Any species that becomes this common is vulnerable to disease and will ultimately be brought under control by natural systems. If Hymenoscyphus fraxineus contributes towards this, then that is not a problem.
Another reason not to worry is that calcareous woods in Shropshire are highly diverse, with species such as Elm (Ulmus glabra), Aspen (Populus tremula), Wild Cherry (Prunus avium), Oak (Quercus robur and Q. petraea), Birch (Betula pubescens and B. pendula), Alder (Alnus glutinosa), Sycamore (Acer pseudoplatanus), Beech (Fagus sylvatica) and Lime (Tilia platyphyllos, T. cordata and T. x europaea) being among the more common canopy trees. If there were a reduction in the vigour of Ash in any semi-natural wood, it is unlikely that there will be any gaps in the canopy for long.
What should I do to prepare for Ash Dieback?
>> If you own commercial forestry and want plantations of Fraxinus excelsior (the only species that is affected by this disease) then you might consider planting different species or waiting until resistant strains are identified. From reports in Eastern Europe, it seems that woods on wet, peaty soils are the most vulnerable. Ash rarely grows on such soils in Shropshire, and plantations in such situations should use other tree species.
>> If you have a semi-natural woodland in Shropshire there is no need to take any action at this stage. It is possible that some trees might die and it could be necessary to remove some standing deadwood for health & safety reasons, but no trees are reported to have died yet and, if they do, then some dead wood is a valuable habitat to leave. The advice from the Forestry Commission is not to fell mature trees in anticipation of the disease, because then you will be removing the resistant ones as well as any that might die.