Park visitors are being warned to avoid sitting, playing or gathering underneath large trees, a fortnight after a seven-year-old girl died when one collapsed on her.
Harrow Council in North West London has issued safety notices after branches were reported to have suddenly fallen at parks in Stanmore, Hatch End and Pinner.
Experts believe the branches collapsed due to Sudden Branch Drop Syndrome (SBDS), which can impact trees such as oak, beech and horse chestnut in dry spells.
The local authority carried out additional inspections of trees in its parks near play areas and outdoor gyms, with none found to be in a hazardous condition.
Despite no injuries being reported in Harrow, officials have put up notices in parks advising visitors not to sit or gather under large trees due to the potential risk.
SBDS can impact seemingly-healthy trees on calm days during the summer, meaning it can be very difficult to predict and therefore poses a safety concern.
While no exact cause has been determined, some experts believe it could be related to moisture levels or linked to bacteria – and that it is more likely in older trees.
Georgie Power from the charity Trees for Cities, which plants and looks after trees, told BBC London: ‘What we think it is, is when the trees are put under huge amounts of stress from dehydration and heat, it’s something similar to self-amputation.
A Harrow Council photo of a fallen tree at Stanmore Recreation Ground in North West London
Harrow Council in North West London has issued safety notices warning visitors to parks
‘So the trees aren’t getting enough water into the branches, and because of that they’re cutting off branches to kind of preserve the rest of the tree.’
London has more than eight million trees, and Harrow is the only council in the UK known to have issued such a notice.
A Harrow Council spokesman told MailOnline: ‘Following recent incidents of fallen branches in the borough, we have a started to carry out additional inspections of trees in our parks near play areas and outdoor gyms – none of which are found to be hazardous.
‘Public safety is our priority, and as a precaution, notices have been placed in parks advising people not to sit or gather under large trees due to the potential risk of a branch suddenly falling.
‘There isn’t a known cause for this – heatwaves and changes in tree moisture levels are considered a possible factor.
‘Trees are vital to our environment and wildlife, and we remain committed to maintaining and growing our tree stock. They provide better air quality, reduce flooding, and is good for mental health and wellbeing. ‘
It comes after a shocking tragedy last month at Chalkwell Park in Southend-on-Sea which saw a seven-year-old girl die when a tree collapsed on June 28.
Seven-year-old Leonna Ruka died after a tree collapsed at Chalkwell Park in Essex on June 28
Leonna died and four other children were injured after the tree collapsed at Chalkwell Park
The ancient tree encircled by a bench as it appeared in the years before its collapse last month
Leonna Ruka, from Dagenham, was killed and four other children were injured after the tree fell while they were enjoying the warm summer weather in the park.
Erena Wilson, 31, was fatally injured in 2012 when a branch fell on her at Kew Gardens
Despite members of the public rushing to try and lift the tree and the efforts of emergency services shortly afterwards, Leonna died from the falling object.
Four other children were taken to hospital, with a six-year-old girl also in a critical condition – and Essex Police have begun an investigation.
In September 2012, a woman was fatally injured when a large tree branch fell on her at Kew Gardens in South West London in what was described by a corner as a ‘ghastly accident’.
Accounts manager Erena Wilson, 31, from Hanwell, was walking through the Royal Botanical Gardens when the branch crashed down on her.
A lawyer representing Kew told an inquest in 2014 that 66million people had visited the gardens over a period of more than 50 years and only one other person had been killed by a tree.
