53 Pa. Stat. § 3292
The commissioners of any township of the first class, or the councils of any borough or city, in the state of Pennsylvania, may, by majority vote in the case of the commissioners, or by joint resolution in the case of the councils, accept the provisions of this act; and when such majority vote or joint resolution shall have been duly passed and approved, and such shade-tree commissioners appointed, or, in their stead, the duties and powers herein provided have been devolved upon an existing park commission, then, from that time and in that event, this act and all its provisions shall be in full force and application in such township of the first class, borough, or city, so accepting; and such commissioners shall be appointed, for terms of three, four, and five years, respectively, and, on the expiration of any term, the new appointment shall be for five years, and any vacancies shall be filled for the unexpired term only; and in townships of the first class the said appointment shall be made by the commissioners thereof; and in boroughs, by the chief burgess, and in cities, by the mayor thereof.
53 P.S. § 3292