Anybody with trees in their care should inspect them regularly, particularly where there could be a liability if injury occurs
Armillaria
roots starting to lift, or trees beginning to lean.
Ganderma
Some very good photographs of the fruiting bodies of a range of decay fungi can be viewed on the website of the Arboricultural Information Exchange at
www.aie.org.uk/index.html - follow the link for tree fungi pictures.
Assessing the Damage
Anybody with trees in their care should inspect them regularly, particularly where there could be a liability if injury occurs. A trained arboriculturalist could be employed to do this, but a simple assessment can often be done yourself, with an expert called in if you have any cause for concern.
The assessment should involve checking the condition of the crown of the tree - if this is done annually it should be noticeable if there is any thinning due to twig or branch dieback, or a reduction in leaf size. Particular attention should also be paid to any trees which are slow to leaf out in the spring, or which shed their leaves earlier in the autumn than neighbouring trees of the same species. Check the trunk and branches for any evidence of bark death, weeping sap or splitting, and for the presence of fungal fruiting bodies. Also make sure that there is no evidence of
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If you have any worries at all it is always best to call in an experienced arboriculturalist (information on suitably qualified consultants in your area can be obtained from The Arboricultural Association, tel. no. 01794 368717). They will then make an assessment of the risk, using a range of techniques. The first will be a visual assessment of the tree, similar to that described above but more detailed and with expert interpretation. If a decay fungus is present they should be able to identify it and assess its significance on that particular tree species.
If the fungus is deemed to be of concern an assessment will then be made of the extent and position of any decay within the tree. This can be done using a number of pieces of ‘kit’. They vary from striking the trunk with a mallet to check the resonance of the wood, through drilling into the tree to take cores or to check the wood’s resistance, to very expensive pieces of sonic equipment that produce a coloured computer image of potential sites of decay. Of course, the expertise lies in the interpretation of the results of any of these tests - a mallet in very experienced hands can give results as reliable as those from a sonic tomograph used by someone lacking experience. It is only possible to be sure of the true extent of decay if a tree is examined after felling.
Taking Action
This is the area where the consultants really earn their corn. Having assessed the threat to the tree they must then formulate a plan of action. This could range from felling the tree to doing nothing, with any number of possibilities in between.
Above:
Rhizomorphs of Armillaria
Left: Sulphur Polymore
The action taken will depend on many factors, including the species of fungus, the species of tree; its location, size, shape and age, and the extent and characteristics of the decay. A good arboriculturalist will have the confidence to leave a tree in situ whenever possible, with felling used as a last resort. In many cases the decay will not be extensive enough to constitute a risk, or will be progressing so slowly that further periodic monitoring is the best option. Even when the decay is extensive this does not always mean that the tree is unsafe. Several of our most significant, ancient trees, for example, have completely hollow stems due to their heartwood having been rotted away, but are still structurally sound. In effect they have become hollow cylinders, an inherently strong structure. It has also
been shown that older trees with thinning crowns may be less likely to be blown over by
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