The Woodland Trust is calling for an immediate mandatory ban across the UK on importing ash trees in a bid to help prevent the destructive disease.
The trust believes the Forestry Commission’s supportive response to the horticultural trade voluntary ban on ash imports is essentially too little too late, and without immediate action the dieback of ash could become the new Dutch elm disease, causing widespread destruction to one of our most common native broadleaf trees.
According to the Woodland Trust, the Chalara fraxinea fungus, which causes leaf loss and crown dieback and can lead to tree death, has already wiped out 90 per cent of ash trees in Denmark in seven years and is becoming widespread throughout central Europe.
Dr Jon Heuch, independent arboricultural consultant and a member of the Forestry Commission’s Biosecurity Programme Board, says that it has taken scientists several years to identify precisely the organism causing the disease: ‘It was thought that the pathogen was already present in the UK, but not causing disease. More recent research has clarified that the disease is present in the UK and thus control measures would both be effective and legally possible.’
A detailed pest risk assessment closes for consultation on 26 October, says Heuch, who is also a member of the Trees and Design Action Group (TDAG) ‘and there’s an anticipation that shortly after action will be taken to to ban ash trees coming in from infected areas, which include all European countries from Scandanavia to Italy’.
The Forestry Commission, he adds, claims that 40% of ash trees planted in the UK are imported. And while ash trees appear to have become increasingly popular with landscape architects in recent years, Heuch knows of no official records being kept of the numbers of semi-mature specimens imported into the UK for landscape purposes. However, the Forestry Commission’s Forest Reproduction Database shows that in 2011, 560,000 bare-rooted ash trees were imported to the UK for forestry purposes. These came principally from Germany, the Netherlands and Belgium, with a smaller number coming from France.
On the forestry side, Heuch adds, seed of the native Fraxinus excelsior ash is frequently sent abroad from the UK and the trees grown from these seeds imported back and sold as having UK provenance. Different species tend to be imported in addition to Fraxinus excelsior for landscaping purposes, he says, yet it appears that these are just as susceptible to dieback.
‘If the fungus becomes established we might expect 80% of ash trees to be killed,’ he said. A ban on imports, he says, ‘if respected and enforced, stands a reasonable chance of preventing its entry.’
There will, however, be some remaining existing stock that isresistant to the disease and could be used to build up ash tree stocks again. ‘It’s not quite the Dutch elm disease situation, although it is still significant’.
It is estimated that 30% of the UK’s wooded landscape is made up of ash trees. It is a species that is excellent for biodiversity, but is also used widely for timber products.