To the maximum extent possible, existing trees and vegetation shall be retained. Trees of six-inch caliper or more and vegetation may only be removed or destroyed as a result of a development, enlargement or site alteration, provided that:

(a)        such trees or vegetation are located in areas to be occupied by buildings, private roads, driveways, areas for required accessory parking, or within a distance of 15 feet of the exterior walls of such building, provided that it is not possible to avoid such removal by adjustments in the arrangement of such buildings, driveways or required parking areas;

(b)        the continued presence of such tree would create special hazards or dangers to persons or property, which would not be possible or practical to eliminate by pruning;

(c)        the continued presence of such tree would interfere with the growth or health of another tree of six-inch caliper or more, designated for preservation and belonging to a species listed in Appendix D (Tree Selection List for On-site Trees) of this Chapter; or

(d)        an authorization pursuant to Section 105-425 (Modification of botanic environment and tree preservation and planting requirements) has been granted by the City Planning Commission approving the removal of such trees or vegetation.

Any tree of six-inch caliper or more that cannot be preserved as a result of a proposed development, enlargement or site alteration shall be replaced pursuant to the provisions of Section 105-32 (Botanic Environment and Tree Planting Requirements).