Forestry Commission scientists have moved a step closer to identifying the cause of a profuse stem bleeding condition which has affected many oak trees in woods in Loughborough, Leicestershire - and they have ruled out 'sudden oak death' as the cause of the problem.
The condition is described as an episode of ‘acute oak decline’. Pathologists from the Forestry Commission’s Forest Research agency have discovered bacteria from three different genera, or "groups", in samples taken from symptomatic trees in the woods. Further tests are now being carried out in a bid to pinpoint which bacteria are responsible for the symptoms, but it could be several months before the exact cause is known.
Dr Sandra Denman, a senior forest pathologist with Forest Research, explained:
"When oaks with stem bleeding were first noticed, there was initial concern that they were suffering from 'sudden oak death', a disease caused by the fungus-like pathogen Phytophthora ramorum, but our tests have confirmed that this is not the case.
"Instead, our initial tests are consistently indicating that bacteria from three different genera, or groups, are associated with the bleeding areas visible on the oak trees at Loughborough. However, we need to do a lot more work to identify the particular species of the bacteria, and to find out the role that each one plays in this episode of acute oak decline.
"Research of this kind is very difficult to do and takes many months, even years, but we are encouraged by the progress we've made so far."
The condition was first spotted in Loughborough's Booth Wood in 2002, when a couple of trees showed symptoms, but by 2007 more than 200 trees were affected. Oaks in the Outwoods were then discovered to have the same symptoms: bleeding cankers and rapid deterioration in health.
Forest Research experts took a number of samples of roots, bark and wood from some of the diseased oak trees in autumn 2007 and March this year. Soil around the affected trees was also taken for analysis in a bid to establish whether the deteriorating health of the trees could be linked to any soil-borne or root-rotting organisms.
Further information about oak decline and sudden oak death is available from the "Protecting trees" area of the Forest Research website at www.forestresearch.gov.uk/oakdecline and www.forestresearch.gov.uk/phytophthora-ramorum.
NOTES TO EDITOR:
- The terms "decline" and "dieback" are used by foresters and arborists to describe a condition in which a number of damaging agents interact with one another to weaken trees and bring about their deterioration, sometimes resulting in premature death. Decline and dieback can be either ‘chronic’ (slow and progressive) or 'acute' (rapid). Damaging agents associated with decline and dieback can 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 few years in succession. In cases of acute decline the trees experience a rapid deterioration in health, sometimes leading to their deaths within as little as four years from the onset of first symptoms. This contrasts with chronic decline, which is a slow deterioration over many years and from which trees can often recover, particularly if there is a reduction in the factors that cause the decline.
- 'Sudden oak death' is a disease caused by the fungus-like pathogen Phytophthora ramorum, which has killed more than a million American native oak trees in forests in California and Oregon. P. ramorum was first identified in Great Britain in 2002, but here (and elsewhere in Europe) its main host plants are shrub species such as rhododendron and viburnum, rather than trees. It produces spores on the foliage of these shrub hosts, and the spores spread to and infect nearby susceptible trees. The indications are that Britain's two native oak species, sessile and pedunculate oak (Quercus petraea and Q. robur), are not very susceptible to P. ramorum and therefore unlikely to become infected. Native beech (Fagus sylvatica), however, is susceptible to it, and lethal bleeding stem cankers develop on infected trees. However, the only beech trees in Britain to have become infected with P. ramorum have always been in close proximity to heavily infected rhododendrons. Further information about bleeding bark on oak trees is available from the Protecting Trees area on the Forest Research website, www.forestresearch.gov.uk.
- The Forestry Commission is the government department for forestry in Great Britain. Forest Research is an agency 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.forestresearch.gov.uk.
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