Following approval of the general plan for a unit of the state park system pursuant to Section 5002.2, all real property which has been designated in the general plan for retention in agricultural use indefinitely as a feature of that unit shall be made available for leasing by the department for agricultural purposes. In addition, any real property which will not be improved pursuant to the general plan for at least three years from the date of approval of the general plan, and which was being leased for agricultural purposes immediately prior to approval of the general plan, may continue to be available for leasing for agricultural purposes if the director makes written findings that use would be compatible with the general plan or until the commencement of improvements thereon.