Cavities and hollows
Most mature trees will contain some cavities and hollows , caused by decay following branch failure or other injury . In general , smaller hollows and cavities do not significantly affect the strength of the timber and are not usually of concern .
Larger hollows or cavities in the stem may present more challenges , particularly if lateral evacuation of a casualty is required and large forces will be applied to the tree structure during the rescue operation . In general , the larger the hollow size , and the larger the
opening in the stem , the more strength will be lost .
As with cracks and splits , the presence of reaction wood may be an indicator that the tree has been able to adapt to the injury and compensate for the loss of strength .
The illustration below provides an approximation of how much strength is lost with different cavity sizes . The arrows show the direction of loading and percentage of original strength in that direction .
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