Deadly disease hits ash trees

LAST week Nature Table (below) featured the ash tree but only days later the news broke that a deadly ash disease had been detected in Ireland.

It’s caused by a fungus called Chalara fraxinea and makes the leaves wither, starting at the crown and progressing downwards until the tree is killed. The first confirmed case in Ireland is in Co Leitrim.

It’s already widespread in Europe where it has been reported from 21 countries. It has killed 90% of the ash trees in Denmark and is spreading in Britain.

About 350,000 hurleys are produced in Ireland every year and the industry supports 400 full-time jobs. About 70% of the timber used is now imported.

The Department of Agriculture has issued a directive restricting the import of live ash plants. They are also in contact with the authorities in the North to establish an all-island strategy to combat the disease. We won’t know the full extent of the infestation until the end of May as the fungus is hard to detect when the tree is not in leaf.

The ash is arguably the most important tree in the Irish countryside because it is such a widespread native species. A biodiversity expert from the University of East Anglia, Chris Panter recently published a statement on the ecological impact of the disease on the British countryside. He cites 80 common insects and 60 rare ones that are dependent on ash and are now at risk. He also lists mosses, lichens, and wood mice as being under threat.

Britain has at least double the amount of native tree species compared to Ireland, meaning the ecological implications of the loss of one major species in this country would be even greater than in Britain.

Ash trees produce copious amounts of seed every year unlike, for example, beech and oak. Also the ash seeds normally stay on the tree, flying off a few at a time throughout the winter. This makes them a reliable winter source of food for birds and small mammals. I have studied a colony of jays in a local wood and they appear to be totally dependent on ash seeds for several months of the year.

I’m also struck by the large number of different tree diseases I’ve been writing about in recent years. It started with Dutch elm disease, then there was an alder disease followed by horse chestnut canker, and now ash die-back. Increased global trade undoubtedly contributes to the spread of new diseases but I wonder about the cause of them.

Nature table

The influx of winter migrant birds is now at a peak.

Many are water birds and the largest, and probably most magnificent is the whooper swan (above).

Between 12,000 and 18,000 spend their winter here and the vast majority breed in Iceland, although the summer range of the species extends across arctic Europe and Asia. Very small numbers stay to breed in Ireland.

The Irish wintering population is of international conservation importance.

The main difference between whoopers and our resident mute swans is that the beak of the whooper is yellow and black.

The whooping call which gives them their name is also unique and there are other small differences.

It’s harder to distinguish them from the slightly smaller Bewick’s swan, a much rarer winter visitor, but a whooper’s beak has more yellow than black and a Bewick’s more black than yellow. Whoopers spend more time feeding on land than other swans do but require open water for roosting.