The Development Bureau tied up the roots of some old trees in Hollywood Road. The old Chinese banyan trees have roots that grow on stone walls. Their roots find a way into cracks between the stones to look for food and water.
Tree specialists say tying up the trees' roots might threaten their survival.
The Development Bureau said they had had complaints about the trees. One person said the roots took up too much space and it was hard to walk along the street.
It is hard for trees to survive in the city. More and more, walls are made less friendly for trees. The cracks are being filled with concrete, instead of mortar. Mortar is a mixture of cement with sand and water. Roots can use mortar, but they cannot use concrete.
The Tree Management Office said about 2,000 trees across the city are unhealthy or at risk.