Get to the root of the problem


his is a case which resulted from a keen observation by a planning officer visiting the site to consider a planning application.  

An oak with existing fungi at the base (small, blackened brackets of Ganoderma) was seen to now have fruiting bodies of a different fungus around most of the base.

With several homes within falling distance of the tree, the potential for damage in stormy conditions was a concern and the owners sought guidance.

An initial inspection from the ground indicated that the tree was in good vigour, with healthy foliage and little sign of dead wood or decay in the branches.  However, the recently appeared fungus, the Beech polypore, indicated cause for concern.  This fungus, normally found on Beech trees, is a sign of decayed roots.  If found on oak, it indicates decay is at an advanced stage.

It is possible to measure the extent of decay in a tree by using several tools.  One of these, a sonic tomograph, works by placing sensors around the base of the tree and sending a sound wave across them.  Sound waves travel faster through a solid material such as wood which has not been decayed, than decayed wood or a cavity.  By measuring the speed of the sound waves as they travel across the wood, the strength of the timber can be established.

The test revealed extensive decay, with only 10% of the trunk being strong timber and 90% decayed.  We normally begin to explore felling a tree when the amount of sound timber is less than 30%!  The risk of the tree failing was very high.  

Marked in green on the bottom right chart is a static assessment of tree stability limit for this tree. From the tomograph we can see extensive decay/cavity, which is identified in blue. Advanced decay is indicated in purple, with the green indicating incipient decay and brown indicating non colonised tissue (sound wood).

Although this tree was a prominent feature in the locality, and it would be missed, work began to fell it, for safety reasons.  Felling was a major project.  It took 7 arborists, 5 trucks and 11 chainsaws, and more than a week to complete!

The team are used to felling decayed and dangerous trees.  However, as work progressed, to their surprise, they found that the trunk was entirely free from decay.  In fact, much of the timber was good enough to be taken to a local timber mill for processing.  They began to wonder whether the root test had been mistaken.  Had this giant tree been felled in error?

With the felling completed, leaving just the stump behind, a contractor with a stump grinder was called to complete the removal.  With baited breath, all waited.  The machine removed the top layer, and beneath was a soft, spongy mass of decayed wood with absolutely NO ROOTS!

All appeared well… at first glance

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The Beech polypore fungus indicated cause for concern.  This is normally found on Beech trees and is an external sign of decay.

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This is the image of the tree at ground level, taken by sonar, indicating the extent of decay. The blue represents no wood at all.

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