Any person or firm given the right to maintain poles and wires in the streets, alleys or other public places in the city shall, in the absence of provision in the franchise concerning the subject, keep such wires and poles away from any trees or shrubs in such places so far as may be possible, and shall keep all such trees and shrubs properly trimmed, subject to the supervision of the superintendent of public works, so that no injury shall be done to the poles and wires or trees and shrubs by contact. (Prior code § 12-2-5)