The call came after 48-year-old Phil Gordon fell from a tree in Abbey Park, Leicester. Gordon, who was also a Green Party town councillor, was taken to Leicester Royal Infirmary, where he died.
Arboricultural Association director Nick Eden said: "I don't know the circumstances, but research has shown fatalities often occur at the end of the day.
"It's important to remain focused all day, not just at the start or the main part of the day. There's a chance you could be tired or rush work towards the end of the day."
Eden said on average five arborists were killed each year, the same number as that of non-tree surgeons killed by falling trees or branches.
Council chief executive Sheila Lock said: "We are all extremely shocked. Phil had been working alongside our trees and woodlands team for just over a year."
The Health & Safety Executive is investigating the accident, and there are no suspicious circumstances surrounding the death. Gordon was one of the city's first Green Party councillors.