Visual Tree Assessment (VTA)
There are a number of published methodologies the professional arboriculturist can follow when inspecting trees. The bottom line is that whichever process is used, it must be a logical, systematic and diagnostic approach.
Additionally the inspection should consider the surrounding environment, in which the trees are growing, with particular attention to the site history and any recent changes.
The most widely used approach, when inspecting trees, is Visual Tree Assessment (VTA), as devised by Claus Mattheck. The assessment consists of 3 stages and compares the tree being inspected to a notional healthy, vigorous and defect free specimen.
It is important to note that even healthy, vigorous and defect free specimens have a natural failure rate.
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The 3 stages of VTA are:
1. Visual inspection of the tree for defect symptoms and overall vitality. If there are no signs of any problems the assessment is concluded.
2. If a defect is suspected on the basis of the symptoms, the presence or absence of that defect must be confirmed by thorough examination.
3. If the defect is confirmed, it must be quantified and the strength of the remaining part of the tree evaluated.
It should be noted that a visual tree assessment is visual only (although it is often undertaken with the aid of a probe, a sounding mallet and a pair of binoculars). The quantification and evaluation (stage 3) may be beyond the scope of a visual inspection and require the use of diagnostic decay equipment and/or a separate climbing assessment.
Three recent court cases have underlined the need for landowners to inspect their trees. The cases provide guidance as to the type of inspection to be undertaken, the level of competence required of the tree inspector and the frequency of inspections.