Deadly ‘Chalara dieback of ash’ disease suspected at Norfolk Wildlife Trust wood in Ashwellthorpe
07:00 23 October 2012
An ancient Norfolk woodland is suspected of being infected with a deadly tree disease which has caused widespread damage to forests throughout Europe.
Officers from the Forestry Commission’s plant health team said Norfolk Wildlife Trust’s (NWT’s) Lower Wood in Ashwellthorpe is “highly symptomatic” of Chalara dieback of ash, a serious disease caused by a fungus called Chalara fraxinea.
Key symptoms, which include blackened dead leaves clinging to branches and purple lesions on stems, have been found at the site near Wymondham, and samples have been taken away for laboratory analysis.
Forestry chiefs said the presence of the disease could not be absolutely confirmed until DNA testing is completed, which is expected to be around the end of this week.
But as about 40pc of Lower Wood is made up of ash trees, conservationists are extremely concerned about the potential effect on the woodland canopy – and on the wider environment if the condition is able to spread.
The NWT’s head of nature reserves, John Milton, said: “This is possibly the first case of ash dieback disease in established woodland in Norfolk, although it is likely we will now see further cases. We are working closely with the plant health team from the Forestry Commission and monitoring our woodlands closely. Tracking the disease is going to be difficult with the imminent autumnal leaf fall, so the true extent of the disease in the UK may be difficult to establish until the spring.”
If confirmed, the NWT site could become Norfolk’s first recorded case of Chalara dieback of ash in established woodland, although the disease has already been found in Suffolk among young trees imported from infected nursery stocks on the continent.
The infection is classed as a “quarantine” plant pathogen, which means the Forestry Commission is able to use emergency powers to contain or eradicate it – with the only available treatment being to destroy plants by burning or deep burial on site.
As yet, no such Statutory Plant Health Notice has been issued to NWT, so Lower Wood remains open to the public, with no special measures implemented for visitors.
But NWT contractors and volunteers are already undertaking biosecurity measures, including not removing materials from the wood and scrubbing boots clean, while visitors have been advised they do not pose a significant risk of spreading any infection if they stick to the paths.
Steve Collin, the trust’s senior reserves officer for woods and heaths, spotted and reported the symptoms at Lower Wood.
He said: “Over about two or three hectares, it has probably affected about 20pc of the trees, and because they are coppiced with maybe 10 or 20 stems each, it is taking a significant amount out of the cover. We don’t know if it is going to kill every single ash in there.
“About 40pc of Lower Wood is ash trees, so we could be looking at some quite significant holes in the woodland cover which is useful to nesting birds. It will take a long time for the wood to recover. We will probably have to alter our management techniques to encourage the regeneration of other tree species.
“The real worst-case scenario is that we could lose ash as a species altogether.”
Lower Wood is one of Norfolk’s few remaining ancient woodlands and a Site of Special Scientific Interest (SSSI). The name Ashwellthorpe, perhaps of Danish origin, hints that the ash trees have been part of the landscape here for more than 1,000 years.
Mr Collin said: “Historically, a lot of our woods in East Anglia have had ash as an important species and a lot of them have been managed for traditional woodland products. It is a strong, light wood which has straight poles and so is very useful for making handles for tools, so culturally it has been very important.”
Steve Scott, area director for the Forestry Commission, said: “Our plant health officers have been out to a number of sites in Norfolk and Suffolk within the last week. What we have found at Ashwellthorpe is highly symptomatic (of Chalara dieback), but will not be confirmed until we have done the lab tests. We had a couple of confirmed cases in Suffolk, which were young trees that were grown on the continent and imported through nursery stocks.
“The implication of that is that it is relatively easy to pull up young trees and burn them, but if it (the disease) gets into the wider environment then it is very difficult to control. But at the moment we are trying to establish if and where there are incidents and then we can make decisions about what we need to do.”
Mr Scott said a letter will be circulated to all Forestry Commission customers this week, warning them of the threat of Chalara dieback of ash trees, and asking them to consider alternate species in tree-planting schemes.
Chalara dieback of ash causes leaf loss and crown dieback and can kill young ash trees very quickly, while older trees tend to resist it until prolonged exposure causes them to succumb.
It is regarded by the Forestry Commission as a very serious potential threat. It has caused widespread damage to ash populations in continental Europe, including estimated losses of between 60 and 90pc of Denmark’s ash trees.
It was unknown in Britain until early in 2012, when the first cases were confirmed in a nursery in Buckinghamshire, on ash plants which had been imported from The Netherlands. Since then, more infected plants have been confirmed in nurseries in West and South Yorkshire, Surrey, Cambridgeshire and Lincolnshire.
Symptoms include blackened dead leaves clinging to branches and black/purple lesions on stems.
-For more information, see www.forestry.gov.uk/chalara. To report potential cases of Chalara dieback of ash, contact the Forest Research Tree Health Diagnostic and Advisory Service on 01420 23000 or email email@example.com.