The term of office of the trustees on the board shall be for a period of three years, except the first trustees on the board, who shall be appointed by the Governor as follows: One trustee for one year, one trustee for two years, and one trustee for three years. Each of the trustees first or thereafter appointed shall be a person who is interested in the preservation, restoration and development of the fort property as a memorial to Nebraska pioneers, and as a reservation to preserve the ideals of Nebraska's early settlers as a state park, or other appropriate historical memorial site. When the respective terms of office of the first trustees appointed to the board shall expire, their successors shall be selected by the county board of the county wherein the fort site or a major portion of the fort site is located; and the trustees appointed to the board shall each hold office until his successor is appointed and qualified.