Landscape Institute member Ian Houlston calls upon fellow landscape professionals to lead prevention of the spread of Chalara diebeback of ash trees
They should do this, he said, by diligently following Forestry Commission (FC) guidance and immediately reporting early signs of the disease. Links to guidance are available elsewhere on the LI website.
This follows the introduction by the government of restrictions, long-awaited by some, on the importation of ash trees into Britain, in an attempt to combat the disease, which is caused by the Chalara fraxinea fungus and leads to leaf loss and tree death.
‘This isn’t something for other people,’ says Houlston, an associate at LDA Design and self-confessed lover of ash trees. ‘This affects all of us; the potential impact on the rural landscape of the loss of this culturally and ecologically significant native tree is profound.’
He urges people to remember the emotive spectacle of majestic elm trees being sawn down in the late 1970s in attempts to curb the spread of Dutch elm disease: ‘People still mourn the loss of Britain’s elm trees,’ Houlston says, ‘and I don’t want to be telling similar stories on the demise of ash trees to graduate landscape architects in 10 years’ time.’
Houlston would like the news of the disease spreading through the UK to galvanise people into action: ‘We can all make a difference, and especially those of us in the landscape profession’.
The FC too is calling on those who work with trees to familiarise themselves with the symptoms illustrated on its website, to inspect their ash trees frequently and report any suspicious cases.
Call for guidance
The Royal Forestry Society (RFS) is calling for clear guidance from the government for woodland owners and managers wondering how to proceed with planting schemes that include ash trees. It is seeking clarification on how movement restrictions will be applied within the UK to existing ash stock intended for planting this winter, and which may have already been granted plant passports.
While welcoming confirmation of a ban on ash imports, and the announcement of task force headed by the government’s chief scientific advisor Professor Ian Boyd, RFS Management Committee chair Andrew Woods warns many woodland owners and managers have been left wondering whether they can go ahead with planting schemes – some of which may have been approved for woodland grants – this season.
Nick Coslett, marketing and sales manager at Kent’s Palmstead Nurseries notes that Chalara dieback has caused damage to ash tree populations throughout continental Europe, specifically to common ash (Fraxinus excelsior) and its varieties, and Fraxinus angustifolia (most commonly used is the Raywood form) is also thought to be susceptible. The susceptibility of Fraxinus ornus, he adds, is unclear and pending further guidance from the Forestry Commission.
Coslett says that his company took a decision several weeks ago not to import ash trees and now only sources those grown in the UK. When pressed to offer a suitable substitute for ash, he suggests the rowan or mountain ash, which also has pinnate leaves, ‘although it does prefer different soils’. He adds that field maples and limes would both make good substitutes in rural and urban settings and that the latter are ‘too-often’ overlooked by landscape architects.
Coslett also recommends that landscape architects in future ‘stick to the Santamour rules’ for urban planting which dictate that landscape architects plant no more than 10% of any species, no more than 20% of any genus and no more than 30% of any family at any one site. In a 2002 paper entitled Trees for Urban Planting: Diversity, Uniformity and Common Sense, Frank S Santamour Jr, from the US National Arboretum suggested that a broader diversity of trees is needed in our urban landscapes ‘to guard against the possibility of large-scale devastation by both native and introduced insect and disease pests’.
The Daily Telegraph last week warned that ash dieback could have been lurking in the UK for years, and that something should have been done much sooner, while The Guardian claims that the government ignored warning details from the Horticultural Trades Association about the disease. An article in the latest issue of New Scientist criticises what it calls ‘the modern taste for instant landscaping, by planting trees hot-housed in southern Europe,’ which, it asserts, ‘has led to plant pathogens arriving in ever-growing numbers’.
Lessons to be learnt
Independent arboricultural consultant and member of the Forestry Commission’s Biosecurity Programme Board, Dr Jon Heuch, is calling for a review, ‘a lessons-to-be-learnt exercise to discover what went wrong and what could have been done better’ despite the enormous effort now underway to identify and control the disease.
Heuch, who is also a member of the Trees and Design Action Group (TDAG), warned in the last edition of this newsletter that the government’s restrictions on the importation of ash trees into Britain have come months too late.
He is now reiterating his concern that plants brought into the UK for non-forestry (ie landscaping) purposes are not recorded and is urging Defra to ‘recognise that a risk based approach for imports from Europe can only work if appropriate skills and capacity are available to undertake risk assessments and the necessary information is available’
House of Commons debate
The Chalara fraxinea outbreak provoked a bitter debate in the House of Commons, where ministers faced questions about why they failed to implement the ban when it was first detected in a nursery in February. It is now believed to have spread to at least 20 sites.
Environment minister David Health has confirmed that 100,000 trees have already been destroyed in an attempt to halt the spread of the disease, and urged members of the public to help.
They are also being asked to use their mobile ‘phones in an attempt to map and help prevent the spread of the disease across the country on a newly created app. The AshTag app, for IOS and Android devices allow users to submit photographs and locations of sightings of the disease.
The first sign of an ash tree affected by the disease is when leaves begins to die at the crown of the tree. The fungus then spreads into the leaf and the stalk, and dark lesions begin to develop at the bottom of the branch.
Suspected cases of ash dieback must be reported: details of how to identify and report the disease and are available on the Forestry Commission website with further information here. The Food and Environment Research Agency has also produced a YouTube clip giving details on the history of the disease.