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New advice for woodland owners worried that their oak trees might be suffering from acute oak decline disease has been published by the Forestry Commission.
Symptoms of acute oak decline include dark fluid bleeding from splits in the bark on tree trunks, and as affected trees approach death there is a notable deterioration of the canopy, or tree tops, and ‘dieback’ of the branches. The condition can kill a tree in as little as four or five years, and it has been found affecting hundreds of trees across central and south-east England and parts of Wales.
Scientists from Forest Research, the scientific research arm of the Forestry Commission, have discovered a previously unknown bacterium which they believe is playing a key role. They are continuing investigations to obtain a better understanding of the disease, how it spreads, and what other factors might be involved. This information will form the basis of appropriate management strategies.
Meanwhile, in response to increasing public concern, they have written a guide, entitled ‘Managing Acute Oak Decline’, which gives advice, based on the knowledge they have gained so far, on how to recognise the disease, what to do about it, and how to minimise the risk of spreading it.
The guide stresses the importance of monitoring the progress of the disease, of limiting access to infected trees, and of disinfecting boots, vehicle wheels, machinery and equipment to help prevent its spread. If an infected tree is to be used for timber, the guide recommends the bark and sapwood be removed and burnt on site, and the logs cut into planks on site before being removed. Planks can be kiln dried at high temperatures to kill any remaining bacteria. It is unknown whether the disease affects timber quality, so caution is advised when deciding how the timber will be used.
The guide also advises against using acorns from infected sites when planting new oak trees, and explains how to report suspected cases to Forest Research’s Disease Diagnostic & Advisory Service.
The Forestry Commission is urging everyone who looks after oak trees to be vigilant and follow the advice in the guide, which was written by Dr Sandra Denman, Susan Kirk and Dr Joan Webber of Forest Research.
NOTES TO EDITOR:
- The oak is an iconic part the British countryside, and widely celebrated in our art, literature, culture and history. It is an important component of our natural environment, and produces some of the world’s finest timber.
- Acute oak decline should not be confused with “sudden oak death” (SOD). Sudden oak death is a term used in North America for a disease caused by a fungus-like pathogen called Phytophthora ramorum which has killed millions of North American native oak and tanoak trees in California and Oregon. Although it is also present in Great Britain, it has mostly affected shrub species and heathland plants, and small numbers of other tree species. Japanese larch trees in the West Country have also been infected with SOD. Britain’s two native oak species, pedunculate and sessile oak, have proved much less susceptible than their American cousins, with only a handful being infected.
- The terms "decline" and "dieback" are used by foresters and arborists to describe conditions in which a number of damaging agents interact with one another to weaken trees and bring about their deterioration, and sometimes premature death. Decline and dieback can be either ‘chronic’ (slow and progressive) or 'acute' (rapid). Damaging agents associated with decline include insects, diseases and extreme weather. Healthy trees can usually withstand sporadic attacks by pests or diseases when they occur singly, but often suffer significant damage if they occur simultaneously or when the trees are stressed by other factors, such as drought or flooding. Decline can also set in when sustained attacks occur over a number of years in succession. In cases of acute decline the trees experience a rapid deterioration in health, sometimes dying within as few as four years of the onset of first symptoms. Chronic decline occurs over many years. Oak trees can often recover from chronic oak decline, particularly if there is a reduction in the factors that cause it.
- The Forestry Commission is the government department for forestry in Great Britain. Forest Research is an arm of the Commission that undertakes world-class scientific research and technical development relevant to forestry. For further information visit www.forestry.gov.uk and www.forestry.gov.uk/forestresearch.
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