Defect does not automatically mean unacceptable risk
A tree displaying a significant defect in an area rarely occupied by people presents a very different situation from a similar tree beside a busy footpath, school playground, car park or building entrance.
Tree risk cannot therefore be considered from condition alone. The nature of the defect, its significance, the likelihood and potential consequences of failure, and what could reasonably be affected all need to be considered.
This reflects the approach advocated by the National Tree Safety Group (NTSG): tree management should be reasonable and proportionate, recognising both the risks associated with trees and the considerable environmental, social and amenity benefits they provide.
Professional Tree Inspection – Visual Tree Assessment
The Visual Tree Assessment (VTA) method described by Claus Mattheck and Helge Breloer in The Body Language of Trees follows a progressive three-stage process:
1. Visual inspection for defect symptoms and vitality.
If there is no sign of a problem, the investigation concludes.
2. If a defect is suspected based on the symptoms, its presence or absence must be confirmed by a thorough examination.
3. If the defect is confirmed and appears to be a cause of concern, it must be measured and the strength of the remaining part of the tree evaluated.
This progression is important. A cavity, fungal fruiting body, crack, abnormal growth or other symptom does not automatically establish that a tree presents an unacceptable risk.
The initial visual assessment identifies whether there are symptoms requiring further consideration. Where a defect is suspected, its presence or absence is established. Where a confirmed defect gives cause for concern, its significance is then evaluated before an appropriate management decision is made.
Where necessary, this may involve further specialist investigation, but the technique used should be appropriate to the particular defect and circumstances.
What does the law expect?
Tree owners have a legal duty of care. This requires them to take reasonable care to avoid causing a reasonably foreseeable risk of harm. What constitutes reasonable tree management will depend upon the particular circumstances, including the condition of the tree, its location and the level of use around it.
The National Tree Safety Group advocates a balanced and proportionate approach to tree safety management, recognising both the risks associated with trees and the considerable benefits they provide.
Trees are natural structures and failures can occur even where reasonable management has been undertaken. The important consideration is whether reasonable and proportionate steps have been taken in the circumstances.
From inspection to appropriate action
The location of the tree and the level of use around it are therefore important. A significant defect in a tree beside a frequently occupied playground, busy pedestrian route or building entrance may require a different response from the same defect in a remote or infrequently occupied location.
Professional inspection is only part of good tree management.
Where an assessment identifies the need for further investigation, remedial work, monitoring or reinspection, those recommendations should be recorded and acted upon appropriately.
An overly cautious approach can result in unnecessary pruning or the premature removal of valuable trees. Conversely, failing to recognise or appropriately manage a significant risk can leave people or property unnecessarily exposed.
Good tree management requires a balanced and proportionate approach.
The objective is to adequately protect people from harm while avoiding the unnecessary loss of the benefits that trees provide. This requires an understanding of the tree, recognition of relevant symptoms and defects, consideration of the people and property that could be affected, and reasonable and proportionate management decisions based upon the evidence.