Ash die-back set to rise
Wales is currently on the edge of the invasion with only 14 sightings (as of 6 Feb), but this will rise in the summer months. Wales has 15,000 ha of ash woodland and it is one of our most common hedgerow trees.
In our response, however, we must make sure the cure is not worse than the cause. The Welsh Government has thankfully resisted initial calls for indiscriminate tree felling.
The long-term objective of any response to ash dieback must be to promote genetic resistance so that ash woodlands can naturally regenerate. According to Finnish and Czech researchers ash die-back does not always kill the trees and they record infected ashes getting better (as well as worse) from year to year, but remark ‘overall development negative’.
Although young ash trees are usually killed very rapidly, older trees can resist the disease for many years. They may eventually succumb, particularly if already under stress from infection. We expect any changes in mature ash woodland to be gradual rather than sudden.
Ash trees are an important habitat in their own right, particularly for specialised fungi, lichens, snails and other invertebrates that thrive on the alkaline bark. Many of these species are almost entirely dependent on ash for survival, so their fate is closely linked to that of their host tree. Ash trees also support many specialist deadwood species like the lesser stag beetle and hole-nesting birds such as owls, woodpeckers and the nuthatch.
Ash dieback could result in significant changes to woodland ecology. As the ash canopy is lost, an initial increase in light levels might benefit some species associated with more open woodland. Many woodland soils, however, are showing increased levels of nitrogen, which favours fast-growing ruderal plants, allowing them to out-compete woodland specialists. Beech and sycamore may become more dominant in many woods, particularly those on alkaline soils. These tree species both have a dense canopy, which could again lead to a loss of species diversity and abundance of ground flora.
A positive aspect of the ash die back story has been it throwing light on the broader question of local provenance and the international trade in “native” species. Between 2003 and 2009 more than 5 million “native” ash saplings were imported into the UK. Even more “native” hawthorn saplings were imported.
The term “native” has come to mean the genetic profile of the seed rather than where it might actually be propagated; a sapling you buy labelled ‘local’ might well be so in origin, but it could still have spent time in mainland Europe.
Ash die-back could be seen as a symptom of a deeper globalisation issue. It’s one reason why the Trusts in Wales have always been keen on local provenance, growing as many seedlings as possible on reserves.
What you can do:
1. Report your sightings – the Forestry Commission website has details – monitoring is crucial and may even help identify resistant populations.
2. If you buy saplings ask if they have spent all their time locally or have they been sent abroad.
(adapted from an article in Welsh Wildlife Spring 2013)