The jury at the inquest into the death of a New Zealander killed by a falling tree branch in London, could not say why the branch fell.
Former Wellingtonian Erena Wilson was killed by the falling branch at Kew Gardens in September 2012, but the coroner's court jury has found there was no identifiable cause of the the branch failure.
Kew Gardens management said the branch fell following squally weather and strong winds, but her family said the branch fell as a result of the phenomenon called "summer branch drop".
The court, in West London, heard three days of evidence and an hour of summing up by Coroner Elizabeth Pygott but found they could not blame summer branch drop, which was suggested as the cause of the accident by the Wilson family legal team led by John McLindon, and their tree consultant Jeremy Barrell.
But her parents did call for research into and greater awareness of the phenomenon, which causes tree branches to to fall when they take up water quickly after drought, stressing them and causing fractures.
Wilson's parents Chris Wilson and Elizabeth Shelley said in a statement: "First we would like to thank the jury for the time and consideration that have given to their deliberations.
"Second, the loss of our darling daughter Erena shattered us as a family and our memory of her is particularly vivid today, as the circumstances around her death are brought to the fore. Our thoughts are not only with Erena, but our hearts go out to all the families that have lost loved ones in similar circumstances.
"Third, event though the jury was not able to determine the cause of the branch failure that killed Erena, our hope is that the circumstances of Erena's death will significantly raise public awareness of the deadliness of the summer branch drop and lead to urgently needed funding and research into this phenomenon.
"If one death could be prevented and one family saved from having to go through this, then some good will have come from this tragedy."
Coroner Pygott summed up for an hour on the third day of the resumed inquest.
The jury had heard that 31 year-old accounts manager Wilson was hit by the falling cedar tree branch. Her friend, fellow New Zealander Tessa Marshall said she heard a "thud" as a branch fell 22 metres on a "yucky day" of weather at the gardens.
Tree experts Dr David Lonsdale, appointed by the coroner, and Barrell, for the family, gave evidence on whether summer branch drop caused the branch failure.
Barrell said the fall was caused by summer branch drop and that if the tree had been pruned the accident would not have happened. He called Kew's tree-risk assessment management system "a shambles and not fit for purpose".
Lonsdale said the system was "robust" and that summer branch drop was ill-defined, but the cause of the branch falling was "akin" to summer branch drop.
Kew Gardens arboretum head Tony Kirkham had said the cause was squally weather of 50kmh wind gusts and 5 millimetres of rain in the hour before the incident.
Kew horticulture director Richard Barley said: "The jury had found that there was no identifiable cause of branch failure from this tree which caused this accident.
"We of course continue to extend our greatest sympathy to the family and friends of Miss Wilson affected by this tragedy. However, we can reassure everybody that Kew places the utmost importance on the safety of its tree collection for all of our visitors and employees.
"And as noted by the independent expert in this case there was nothing that could be foreseen, the were no actions, that he felt could or should have been taken and that the trees were being managed in an entirely appropriate and responsible way.
"Summer branch drop is a very loosely-defined phenomenon. It's not well researched and there's very little data on it and hence I think it is unfortunate to seek to, as in this case, to make something fit that loose definition."