When a vacancy occurs on the Board of Park Commissioners by reason of death, resignation, change of residence from the city, failure to remain a freeholder of the city or due to any other cause, the remaining number or members of such Board shall appoint a successor or successors, or if there should be no members left on such Board shall appoint successors, and in either event, the appointments shall be for the unexpired term or terms.
('71 Code, § 143.06)