WHY IS IT HAPPENING?
Recent publicity about the arrival of the fungus Chalara fraxinea causing leaf loss and crown die back in ash trees, normally leading to death of the host, follows hot on the heels of other tree diseases that have recently established in Britain.
Analysis of confirmed cases, numbering around 300 country-wide, and with one case in a Surrey nursery, suggests that while many can be attributed to importation of plant material from Europe, it is quite probable that others are caused by natural dispersal mechanisms, on wind or the feathers of birds from overseas; indeed just over half the confirmed reports relate to situations in the wider environment, with no obvious relationship to tree nurseries or recent plantations.
Irrespective of how these infestations find their way to our shores, there is no denying that they are on the increase: digging deeper into the Forestry Commission website, we are reminded that since the onset of Dutch elm disease in 1971, there have been 20 unprecedented threats on our tree population; 16 of these have occurred over the last 10 years, and of these, 6 have occurred within the current decade which has really only just begun. The rate is clearly increasing and research indicates climate change will continue to create conditions for more pest and disease activity.
Some of us might welcome the advent of climatic conditions more typically attributed to the west and north-west France, but it seems there will be a price to be paid in loss of some tree species from our landscape.
HOW DOES IT AFFECT THE TREE?
The fungus attacks the tree just under the bark causing distinctive diamond shaped lesions. The leaves wilt and gradually turn black or dark brown in colour looking like it has been frosted. The branches of the tree die back from the top of the crown. In young trees the effects of the disease are recognisable in the stems which exhibit a transition from green at the base of the tree, through purplish brown to black.
HOW WILL IT AFFECT THE LANDSCAPE?
Ash and oak are the dominant tree species in most of the Surrey woodlands and there is no doubt that the changes will be significant with large gaps appearing in woodlands and roadside verges.
Funds that are normally spent on improvements to the Surrey landscape will need to be diverted to dealing with thousands of dead trees but we must remember the storms of 1987 and 1992 when just this sort of natural disaster was thrust upon us. The landscape will slowly recover and resistant trees will thrive in woodlands and be developed in tree nurseries.
WHAT CAN WE DO?
We know that the spores of the fungus spread in summer months (June to September) from the leaves of infected trees. It is therefore important not to transport the leaves of affected trees from their existing site, and if possible they should be destroyed by burning on site. There are murmurs in the tree industry about the removal of a proportion of Ash before they are infected to allow the use of the timber. The problem with this is it is reported that a small percentage will be genetically resistant and we could be removing some of this valuable genetic material.
Rob Davies, Woodland Officer, Surrey Wildlife Trust, said on their web site, “We broadly welcome the Government’s interim Chalara Control Plan.
“Our belief from the start was that a science-led and precautionary approach should be taken to addressing the disease, and one with wildlife and ecology at its heart. The cure must not be worse than the cause. We are pleased that Government has taken this on board.”
We can also help by being aware of the possibility of the disease, monitoring woodlands and trees, and reporting suspected cases as soon as possible.
The Forestry Commission and others are working hard to reduce the rate of spread, develop resistance to the disease in native trees, encouraging landowners and managers to take action to assist with monitoring and control of the disease, and developing environmental and economic resilience to the effects of the disease.
WHO TO CONTACT
If you think you have spotted the disease, please check the Forestry Commission’s symptoms video and symptoms guide, and their guide to recognising ash trees, before reporting it to the Chalara helpline: 08459 33 55 77 (open 8am – 6pm every day) or email@example.com
For more information on Chalara fraxinea and other tree disorders, visit: