If any town, city, county, or village district decides that the above powers shall be exercised by a recreation or park commission, it shall consist of citizens of such town, city, county, or village district. In cities the citizens shall be appointed by the mayor or city council, subject to provisions of the city charter; in towns by the selectmen; and in other political subdivisions by the governing body of the subdivision. The persons initially appointed to the commission shall serve staggered terms. Their successors shall be appointed under the same appointing procedure for 3 years. Vacancies as they occur shall be filled by the appointing authority for the unexpired term. Any city or town may by ordinance or resolution provide that the mayor or a selectman, or councilman, shall be an ex officio member of the commission.