Caring for the enormous Copper Beech tree towering over the South Nave Transept and an elderly tree in the Precinct requires a specialist tree inspection.

One of the largest trees of the Precinct, the Purple Beech off the South Nave Transept requires particular specialist care.

The Cathedral commisions Down To Earth and Harroway Trees to carry out decay evaluations on two mature trees within the grounds of the cathedral and report on their current structural condition. The full 2020 report is available here

Purple beech tree

The tree is approximately 22 metres in height, assessed by eye, and located close to the fabric of the Cathedral building. The removal of a large limb many years ago at a height of approx. eight metres on the south east side has led to the formation of deterioration of exposed wood within the wound. At the time of my previous visit, a small group of fungal brackets were present on the surface, indicating colonisation with Polyporus squamosus, a common cause of white-rot on trees of this species.

On the first occasion the Resi was used in four locations directly below the wound to indicate the extent of decay in this direction. The results revealed a significant area of decay below the lower level of the wound which diminished to just a small zone of incipient decay by the fourth measurement, some 50cm below the wound.

Each of the measurements record the onset of advanced decay/hollowing at depths of 15cm, 12cm and 23cm on the south side of the wound and 9cm, 18cm and 19.5cm to the north, including the initial narrow bark layer. Some of the drillings autoretracted before the 40cm maximum drilling depth, due to lack of lateral support to the drill within advanced decay or more probably hollow areas.

Each measurement shows a momentary rise in drilling resistance before abruptly dropping as the probe enters decay. This indicates that the area of deterioration is surrounded by a ‘boundary’ layer of wood, produced by the tree’s natural defence system, effectively minimising the development of further incipient decay beyond its current extent.

The current set of results, coupled with the previous ones, indicate that a significant area of decay has formed as a result of the original pruning wound. The stem at this level is sufficiently broad to minimise the likelihood of wholesale fracture at this level, in my view. However given the tree’s location it would be prudent to carry out careful reduction of the crown, as a precaution against future failure of the limbs directly above the wound.

It is recomended to carry out crown reduction, following receipt of all necessary consents; repeat an aerial evaluation of the extent of decay in three years and consider the requirement for further crown management at that time.

Common sycamore

The tree is formed by two diverging stems (identified as west and east) supporting an irregular-shaped crown; although the stems form a union at a height of one metre it is possible that each stem was originally established as an individual plant. The tree is obviously of great age and size, the crown rising to at least 25 metres. This assessment has been prompted by appearance of fungal brackets (also indicating P. squamosus) on the west stem at the base of a dead, deteriorating branch stub. Large areas of bark deterioration were also evident in the vicinity.

A further indication of dysfunction became evident at the base of the joint stem on the south side in the form of a large group of toadstool-shaped fungi; although deteriorating by the time of our inspection, I understand the group has been identified as probably representing the presence of Armillaria tabescens, a form of Honey Fungus. Although rare in my experience, referencing other authorities indicates that it is currently confined to the south-east of England, although more common in Europe. Similar to other species of Honey Fungus it is prevalent on trees already stressed by other agents.

In view of presence of these fungi a precautionary assessment of the base of the joint stem was carried out using a Picus sonic tomography unit. A total of 18 measuring points were used (small nails inserted through the bark to make contact with the woody surface beneath) at an approximate height of 10cm above ground level.

The principal feature identified by the Treetronic result is a diagonal band of unusually high electrical resistance in the central stem (coloured dark maroon), suggesting an area of hollowing or other physical barrier to the induced electrical voltage.

The area between the two stems was water-filled at the time of inspection but probing with a thin steel rod indicated that it extended easily some 60cm down the stems (see photo) and it appears probable that the area of high resistance shown above is linked to the original union between the stems. A Resi measurement appears to support this view.

With regard to the stem above, a nylon-headed hammer was used to check the resonance produced through the bark, resulting in a number of large areas being identified, almost exclusively in the vicinity of the stem exhibiting the fructification. Small areas of bark were excised with a chisel to reveal the presence of white fungal mycelium within the bark. This suggests its deterioration may be a symptom of Honey Fungus colonisation. One small area near the base of the east stem also revealed similar mycelium in a piece of inner bark.

The crown on the west side is supported by two long, leaning stems from which numerous lower limbs have been removed previously. Some of the resultant wounds appear to be deteriorating and a cavity is clearly visible on the ascending limb on the south side. A photo on page 11 shows the general arrangement of the crown west side.

A number of supporting cables have been installed, linking these limbs with anchor points within the east crown. The method of attachment of these cables (throughbolting or partial depth screw eyes) could not be determined from ground level or the general condition of the cables themselves.

Recommendations are to consider reduction of two leaning limbs on the west side and monitor the tree’s general condition regularly. Further investigation may be appropriate in three years’ time or sooner depending on external symptoms of decline.

Summation of 2020 Tree Inspection Report by John Harraway, Harraway Trees

Full report

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