Damage in Beech from flush cuts

Fig 6.1. The full form of the Beech can be seen at the traffic light corner of a busy highway with the main weight of the canopy leaning towards the highway.

This final case looks at a Beech tree, Situated on the corner of the B6157 and Otley Road in Leeds (Fig 6.2). This is an extremely busy highway with almost constant flow of traffic throughout the day (see Fig 6.1). Due the continuous presence of numerous high value targets, any defect found within the the tree is accompanied by a high factor of risk and must therefore be treated with caution. At first glance the tree would seem in good health, as a mature specimen with a substantial well formed crown. However, at closer inspection there are a number of apparent wounds that are emerging as a result of flush cuts from poor previous pruning work. 

Optimum pruning cuts should occur in line with the collar or branch bark ridge as opposed to a stub cut, where too much wood is left, or a flush cut, where too much wood is removed (Lonsdale 1993). When cuts are made behind the branch bark ridge, as seen in Fig. 6.4 and 6.5, it removes the protective boundaries which allows microorganisms to proliferate more quickly into the tree stem (Shigo, 1984).

Fig 6.2. The Beech tree can be found directly opposite Salvo’s (centre left of map) on the corner of Otley Road and B6157.
Fig 6.3. the Beech can be seen to be leaning towards stationary traffic at the traffic lights.
Fig 6.4. Multiple wounds that have failed to heal over can be seen here as a result of previous flush cuts -poor pruning practice. Some of these have developed significant holes containing dead wood which will affect the translocation of sap and in turn weaken the branches.
Fig 6.5. The largest wound, as a result of a flush cut, whereby a large cavity approx 35cm in diameter has developed. The concern is that this creates an opening for fungal invasion and that the stem will become, or has already become compromised. Because of this, an advanced survey producing an acoustic tomograph of the stem directly beneath this wound is recommended. A reading should also be taken at the base of the tree to gain a more complete picture of stem quality. Practically speaking, taking a tomograph reading at approx 2.8m up will be quite difficult, and may be advisable to do so from a work platform.

In this case, prescribing a recommended treatment would be premature due to lack of quantitative information on the trees health and stability so instead a recommended set of investigative actions should be followed in order to best prescribe a treatment, if any at all. There are a number of flush cuts throughout the tree canopy that may weaken branches at various points. An aerial inspection of these limbs with a knife and probe to assess the extent of decaying wood in these wounds would be the first recommended action. The largest wound occurs where the crown meets the stem, as seen in Fig 6.5 and is host to a large amount of dead and decaying wood. Because of this, the recommended action would be to carry out a quantitative assessment of the trees structural properties, just beneath this wound, using an acoustic tomograph (see Fig 6.5). Due to it’s visual prominence and mature status this would be considered a high value tree and every effort should be made to retain it, if viable. Despite being costly and time consuming we can conclude that the recommended assessments would be entirely worthwhile given the high value of both the tree and targets concerned. That this tree has not become of note to Leeds City Council (Dracup, 2008) also supports the argument that scheduled surveys of urban tree populations would be of benefit to a revised and imposed British Standard regarding tree safety inspections (BSI, 2008).