In addition to the general requirements of Article 26 of this Title all new development, or substantial modifications of existing development, in the "R-H" zone shall hereinafter be subject to the following additional requirements which are intended to preserve and extend the visual quality of the neighborhood.
(a) Existing street trees three inches or greater in trunk diameter shall be preserved where practicable.
(b) Where preservation is impractical, and existing street trees three inches or greater in trunk diameter are removed to accommodate new construction, replacement trees of similar type and future mature size shall be installed during the next seasonal planting period. Street tree replacements shall be required on a one for one basis.