All required landscaping and structural features, whether in existence on the effective date of this title or installed after said date, shall be maintained in a healthy and attractive condition. Maintenance shall include but is not limited to watering, fertilizing, weeding, cleaning, pruning, trimming, spraying and cultivating. For purposes of enforcement, the occupant of the property, whether he be the owner, lessor or tenant, shall be responsible for such maintenance. In the case of a vacant building the owner shall be responsible for such maintenance. Replacement of dead, dying or damaged plants, shrubs and trees shall be in conformance with the original approved landscape plan. Prior to the reoccupancy of a building with existing landscaping all portions of damaged or defective irrigation systems, dead, dying or damaged turf, plants, shrubs and trees shall be replaced. Any significant alteration of an approved installed landscaping installation (such as the removal of mature trees) shall be approved by the Planning Director. Removal of mature trees may only be approved if the tree is dead, in danger of causing bodily harm (by falling or dropping limbs) or damaging property.