Tree Risk Assessment on Major Beech…Shock Discovery!

Tree Risk Assessment on Major Beech…Shock Discovery! I was called out last week to carry out a risk assessment on a major multi stem Beech tree. A massive tree indeed! DBH (stem diameter) was 1.49 metres with crown radius of about 10 metres and height approx 19 metres. 4 massive stems had grown out of the main stem from approximately 3.5 metres. One of these was leaning over a public park area which at a height of about 5 metres was found to have a large spectacular growth of Pleurotus ostreatus – Oyster Fungus. This particular fungus not only causes lignin degradation but also can cause cellulose degradation resulting in a major loss of structural strength. A review using QTRA methods assessed the target value relating to numbers of people passing on a daily basis, the size of the actual stem and a high probability of failure. The result was an unacceptable risk of harm. However further investigation resulted in a shocking discovery! At the base of the stem, a small hole was found within extensive reactive basal growth. A cavity was suspected! Testing with a 90cm probe, the probe completely disappeared inside with a major cavity of at least 1-metre diameter! Using Matthecks R1/R2 formula resulted in a measure of 0.71 indicating a high risk of failure! Unfortunately with the tree overlooking public space the level of risk is too high to ignore. Had the tree been in woodland, the risk level would have been tolerable. The importance of a thorough assessment cannot be emphasised enough. Interestingly, it was the fungal fruit bodies that raised the alarm! QTRA (Quantified Tree Risk Assessment) procedures provides a measurable and reliable risk assessment and the current Autumn season is an excellent time to review tree risk.

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