The commission shall consist of not less than 3 nor more than 7 members. In a town which has a planning board, one member of the commission may also be on the planning board. In a city which has a planning board, one member of the commission may be on the planning board. In cities, the members of the commission shall be appointed by the mayor subject to the provisions of the city charter, and in towns the members of the commission shall be appointed by the selectmen. Alternate members may be appointed in a like manner and when the alternate serves in the absence or disqualification of a regular member, the alternate shall have full voting powers. When a commission is first established, terms of the members shall be for one, 2, or 3 years, and so arranged that the terms of approximately
1/3 of the members will expire each year, and their successors shall be appointed for terms of 3 years each. Any member of a commission so appointed may, after a public hearing, if requested, be removed for cause by the appointing authority. A vacancy occurring otherwise than by expiration of a term shall be filled for the unexpired term in the same manner as an original appointment. Members of a conservation commission shall be residents of the city or town which they represent. Members of a conservation commission also may serve on other municipal boards and commissions, including, but not limited to a historic district commission established under N.H. Rev. Stat. § 673:4, and a heritage commission established under N.H. Rev. Stat. § 673:4-a.