In addition to the applicable underlying street tree planting requirements, tree planting provisions shall also apply to extensions or alterations, other than incidental alterations, involving 30 percent or more of the existing floor area of a building. Notwithstanding the provisions of Section 43-02 (Street Tree Planting in Manufacturing Districts), all developments or enlargements within the Special Clinton District that include uses listed in Use Group 17 or 18 shall provide street trees in accordance with Section 26-41 (Street Tree Planting).