A death linked to that of Erena Wilson, who was killed by a falling branch in Kew Gardens in 2012, should not be taken as a precedent, according to arboricultural consultant Bob Widd.
Summer branch drop has been linked to Wilson's death, caused by branch from an 18m-tall Lebanese cedar at Kew in September 2012.
Widd was the coroner's expert witness in a 2011 summer branch drop case concerning the death of Sophie Howard in Peterborough. Yaxley Parish Council paid her family compensation in an out of court settlement.
Widd and two other tree experts - David Brown for the council and Frank Hope for the Health & Safety Executive - agreed on the cause and blamed the council for poor tree management. The coroner recorded a narrative verdict after he was told 11 trees were found to be a "high-risk" hazard that required immediate removal.
But Widd said: "The case was different to Kew because Kew is managed on a daily basis in a professional manner but the council had no reports, surveys or policies."
He said suggestions that Kew should have had signs warning of summer branch drop and cordoned-off areas were going too far. "Six people a year get killed by falling trees in the UK - that's a one in 10 million chance. If you put up signs at Kew saying 'don't walk under trees' because it's dangerous, where do you stop? Risk has to be managed properly. "
An Arboricultural Advisory & Information research note detailing summer branch drop was cited by tree expert Jeremy Barrell in the Wilson case.
Widd said the phenomenon hits predisposed mature trees that could include cedar after heavy rainfalls following prolonged drought. Branches become "like a central heating pipe with a crack then you turn on the water and it blows", he explained.
Fatal branch fall - Inquest opens at West London Coroner's Court
A fatal branch fall may have been caused by "summer branch drop", an inquest at West London Coroner's Court heard last week.
Assistant coroner Elizabeth Pygott said her probe would "firmly focus" on whether proper pruning would have prevented Erena Wilson's death and whether summer branch drop was the cause.
Wilson's barrister, John McLinden QC, told the inquest: "It was just a fluke that there was not more than one fatality or that other people did not suffer very serious injury."
He said Kew had previously taken steps to protect the public from falling branches by issuing warnings and cordoning off areas. "These steps seem to have fallen away, for reasons that the family do not know."
But Pygott rejected a report for the family by consultant Jeremy Barrell that brought up summer branch failure and the Howard case. She commissioned an independent report but said Kew arboretum head's report can be given as evidence when the inquest restarts.