The owner of trees has a legal duty of care to the public at large and his neighbours to act in a prudent and responsible fashion.
In the furtherance of this duty an owner of trees should carry out regular inspections, such as on a yearly basis, in order to detect any significant change in health or the presence of any weakness or decay, which could lead to instability.
Should s/he not be competent for this, or be in any doubt, s/he should employ a specialist consultant. If an inspection reveals no apparent weakness or decay and a tree, or part of it, subsequently fell causing damage or injury, the owner would not be held to be guilty of negligence if the weakness was hidden or not detectable. On the other hand, if an inspection was not carried out and the problem could have been detected, then the owner could be held liable for the consequences.