The UK could be facing a repeat of the impact of Dutch elm disease among its native ash trees without immediate action to stop a destructive fungus spreading from Europe, conservationists have warned.
The Woodland Trust is calling for a mandatory ban on the import of ash trees from outside the UK to stop Chalara dieback of ash becoming established here.
Without a compulsory ban on imports, ash dieback could become the new Dutch elm disease, causing widespread destruction of one of the country's most common native broadleaf trees, the trust said.
The Chalara fraxinea fungus, which causes leaf loss and crown dieback and can lead to tree death, has wiped out 90% of ash trees in Denmark in seven years and is becoming widespread throughout central Europe, the Woodland Trust said.
Ash trees make up an estimated 30% of the UK wooded landscape, across woodlands, parks and hedgerows, are good for biodiversity and are traditionally used for making furniture and tools and creating quality firewood and barbecue charcoal.
Young trees with the fungus have been found this year in six nurseries and four planting sites in England and Scotland.
The Horticultural Trades Association (HTA) has called for a voluntary moratorium on importing ash trees, but warned that given the widespread trade in plants across Europe it was almost inconceivable that the disease was not already established in the UK.
The HTA said it had raised the issue back in 2009, requesting imports be prevented, but was told quarantine action could not be taken because the disease was already present and widespread in the UK.
The voluntary ban has been welcomed by the Forestry Commission, which earlier this month launched a consultation on a risk assessment of the disease which looked at how it could be eradicated and measures to prevent further outbreaks.
But Norman Starks, UK operations director at the Woodland Trust, said: "This is not the time for weak ineffective voluntary embargoes; we are calling on governments across the UK to put in place an immediate and compulsory ban on imported ash before it's too late."
The longer the UK waits to bring in a compulsory ban, the closer the country comes to seeing a landscape without ash trees, he warned.
"As an island we have a great opportunity to stop the spread to the UK by closing our borders to this disease. If the disease takes hold the cost and safety implications regarding the removal of infected ash trees would be huge.
"Many of our tree diseases have originated from imported species and in some cases, for example Phytophthora ramorum which is wiping out larch trees across the UK, it's a battle that is already in full swing.
"We are in a position to stop this war in its tracks before it has the chance to take a hold. It is also an opportunity for the UK industry to capitalise on this and grow disease-free UK ash trees for the UK market."
The Forestry Commission said it was consulting on what measures to put in place to protect the trees, with proposed options including legislation which would ensure ash trees were only imported from areas free of the fungus.
Nick Mainprize, deputy plant health manager at the Forestry Commission, said of the disease: "We are very concerned because we are well aware of what's happened in northern Europe, where it has travelled very quickly in under 10 years."
He said Denmark had lost 90% of its trees, and warned: "We anticipate something similar could happen in this country."
While the consultation is taking place, the Forestry Commission is surveying for the disease, which has not been found in the natural or wider environment outside nursery or recent planting sites.
Infected plants and those on the same consignments as them are being destroyed.