Britain's sycamore trees under threat from bark disease

FIRST, the vast majority of the UK’s 20 million elm trees were wiped out by the catastrophic and preventable introduction of Dutch elm disease. Then, last year, a crisis centre for dealing with sudden oak death was set up at Forestry Commission Scotland headquarters in Edinburgh, to safeguard the oak woodlands of western Scotland.

Now the Arboricultural Advisory and Information Service (AAIS) has sent out a warning that Britain’s sycamore trees are at risk of sooty bark disease (SBD).

Last year’s hot, dry and late summer has caused abnormal stress to many of the country’s oaks, leaving them more susceptible to pathogens which have a better chance of success on weakened trees.

If climate change warnings are borne out and the UK continues to experience the early arrival of spring followed by a prolonged hot summers and mild winters, the number of sycamore trees, a cousin of American maples, may be significantly reduced, according to the AAIS.

Dr Jean Webber, a tree pathologist with the Forestry Research, an agency of the Forestry Commission, said: "This fungus is what we call a latent pathogen - it can sit within the wood of a perfectly healthy tree for many years, still alive but not active. Then, when the tree is under a period of stress, particularly after we have a severe drought, it is able to gain the ascendency and bring the tree into a state of decline. When it manages to do that it is able to fruit, and we are able to see the nature of the disease on the bark, which it kills and causes large amounts to fall off."

Experts say that the number of sycamore trees that will die from SBD will depend on this year’s weather. If this summer is hot and dry, the more advanced stages of the disease will become visible: as well as dead bark, the crowns of infected trees start wilting and the leaves will fall off before autumn.

SBD typically enters a tree through damaged bark or a break in a leaf stem. There is no treatment, making SBD impossible to prevent.

Dr Webber added: "The main recommendation is that if you are planting sycamore then you need to make sure it is mixed with other species so if you do lose them you don’t lose a whole tract of them in one area.

"It is really a case of accepting that this is something we will see with a hot summer, and, of course, if we are moving towards climate change with warmer summers, it may become more of an issue.

"People may then want to consider how much sycamore they want to plant in this country. It is about balancing the trees that we plant. Nowadays, no-one would think of planting a lot of elms."