When performing advanced risk / structural assessments on trees, the logical first step is to ascertain the amount of remaining soundwood in the trunk and scaffold branches and if this is enough to bear the trees load long term. No parameters for tree removal have been mentioned in this website because no “rule of thumb” has been agreed upon in the Arboricultural industry. Rather the author has concentrated on how the tree reacts to this decay.
Identifying the robust formation of wound wood to counter internal decay is a powerful tool in deciding if a tree should be removed or retained. Additionally, multiple visits to a tree may be required to assess the speed at which decay is progressing. The author hypothesises that a strong wound wood response will mean that the tree is also aggressively compartmentalizing decay internally as well.
Due to the differing decay patterns among fungal species and the irregular geometry of sound wood / decayed wood in the trees cross section that ensues, the author believes that most engineering-based modelling of tree strength and stability can be disregarded. Rather, the arborist should gain knowledge of the host tree / fungal interactions as this information is critical when specifying if a tree should be pruned, removed or supported with cabling.
Reduction pruning may be deemed necessary to mitigate against branch or crown failure but remember that little is known about the effect of pruning on tree health or structural stability and it must be remembered that pruning (no matter how little) will cause some level of disfunction in a tree’s physiology.
In older trees, the installation of support cabling can reduce the need for excessive pruning and loss of foliage whilst still mitigating against the risk of failure from internal decay.
I hope you have found the information within this website both interesting and informative. Please feel free to contact me regarding any aspect of tree risk management you wish to discuss.
Managing Tree Risk 101 