(a) The department shall plant and care for a substantial number of pecan trees on United States and state highway rights-of-way throughout the state.
(b) In an area where the climate is unsuitable for pecan trees or where pecan trees present a safety hazard, the department shall plant other indigenous or adaptable trees that do not present a safety hazard.
(c) The cost of acquiring, planting, and caring for the pecan trees shall be paid from the state highway fund.