A local council has urged residents not to sit underneath or near trees after large branches spontaneously fell down.
Harrow Council has issued safety notices after branches fell in Standmore, Hatch End and Pinner parks in north-west London. There were no reported injuries.
The council says the issue is down to Sudden Branch Drop Syndrome, which has no known cause. Heatwaves and changes in tree moisture are believed to be a factor.
“Some incidents of sudden branch drop have occurred in the borough during the June heatwave,” the notice read.
The council has carried out additional inspections of trees in all the parks, as well as near play areas and outdoor gyms.
They have not found reason to believe any additional trees are hazardous, but have asked the public to be aware of the issue and to report any concerns via their website.
“Trees are vital to our environment and wildlife, and we remain committed to maintaining and growing our tree stock,” it added.
“They provide better air quality, reduce flooding, and are good for mental health and wellbeing.”
Sudden Branch Drop Syndrome typically affects large trees such as oak, beech and horse chestnut.
It usually occurs after a long, dry spell followed by a sudden downpour of rain. The branches then fall in subsequent, calm conditions.
In 2012, a woman was killed at Kew Gardens after the branch of a tree suddenly fell on top of her in the Royal Botanical Gardens.
Kew Gardens described the incident at the time as a “terrible freak accident”.
