And to reply to the original question.
The housing officer will know who is responsible for the trees. Well they will know if its tenants or HA's responsibility.
As for who owns the trees. Anyone think the housing officer may not know?
If its in a neighbours garden its the neighbours responsibility. If its public land chances are its the councils responsibility. Sometimes with contested boundaries its not black and white who owns the trees. But may I also state that every tree does have an owner.
Would it be a reasonable request of a housing officer to spend days on one small case trying to find out who owns the trees?