Can we rely on an expert witness telling us what the courts are expecting when it comes to tree risk?
In short, the answer is no because they’re an expert to the court, and not an expert for the court.
A competent arboricultural expert witness knows their limitations. Namely, their role is limited to being an expert to the court. They’re stepping way outside their field of expertise if they claim a Judge’s wisdom about how the law will evaluate tree risk-related evidence in the next case.
Claims by Arborists that they’re experts for the court should ring alarm bells. In a similar way to a Judge who, with no arboricultural training or qualifications, claims they could carry out an advanced tree risk assessment with a Static Load Test on a tree that has extensive root decay because they’ve seen it done.
In the UK, we’ve had several tree risk-related Judgments where the Judge has spotted an expert straying outside of their lane, and dipping into their legal dressing up box. Most recently in Colar v Highways England.
What’s of much greater concern is when a Judge is not aware that the evidence an expert gives them is critically short on expertise. Highly questionable expert evidence appears to have been pivotal in two landmark Judgments in the UK, Poll v Bartholomew and Cavanagh v Witley Parish Council.
This article explores the gulf between reasonable, proportionate, and reasonably practicable tree risk assessment and management, and expert evidence in these cases.