Any vegetation that cannot be saved as a result of site alteration, enlargement or development shall be replaced with alternative vegetation to be approved by the City Planning Commission. All developments, enlargements and site alterations shall comply with the tree planting requirements set forth in this Section, whether or not existing trees are removed as a result of such development, enlargement or site alteration.

The replanting of elements of vegetation that are parts of an association or community shall be such as to reestablish, as rapidly as is reasonable, the vigor and character of the association. When necessary to establish ecological balance, the Commission may also require additional vegetation to be planted.

(a)        Tree planting

For the purposes of this Section, the following minimum standard shall apply for tree planting:

(1)        For any development, enlargement or site alteration within a Special Natural Area District, trees of at least three-inch caliper, pre-existing or newly planted, shall be provided on the zoning lot at the rate of one tree for each 1,000 square feet of lot area or portion thereof or shall equal a total of 51 percent of all tree credits for trees originally on site, whichever is greater.

(2)        For any existing tree of at least six-inch caliper that is preserved, credit for one tree shall be given for the first six inches of caliper and, for each additional four inches of caliper, credit for an additional tree shall be given.

Single-trunk trees, newly planted to meet this requirement, shall be of at least three-inch caliper at the time of planting. Multiple-trunk trees and low-branching coniferous evergreens shall be at least 10 feet in height at the time of planting. Trees newly planted to meet this requirement shall be of a species selected from Appendix D of this Chapter, and acceptable from the standpoint of hardiness, appearance and habit of growth suitable to the site.

The Commission may grant a waiver of the tree planting requirements by certification to the Department of Buildings, where the Commission finds that the ecology of the site is such that the substitution of other plant material would be more appropriate than the tree planting requirements and a detailed plan for planting has been filed with the Commission for its approval.

(b)        Botanic Environment Planting

For the purposes of this Section, the following minimum standard shall apply for the planting of vegetation.

Any vegetation or topsoil that cannot be preserved as a result of a proposed development, enlargement or site alteration and is not permitted to be removed pursuant to the regulations of Sections 105-31 (Botanic Environment and Tree Preservation Requirements) or 105-425 (Modification of botanic environment and tree preservation and planting requirements), shall be replaced as follows: for every square foot of lot area of removed vegetation or topsoil, plantings shall be provided of the size and number indicated in paragraphs (b)(1), (b)(2), (b)(3) and (b)(4) of this Section. The area of removed vegetation shall be measured so as to include any portions of the zoning lot that were located within the critical root zone of a removed tree of six-inch caliper or more. Species of ground cover and shrubs shall be selected from Appendix C (Selection List for Ground Covers and Shrubs) of this Chapter. Species of on-site trees shall be selected from Appendix D (Tree Selection List for On-site Trees) of this Chapter.

(1)        Ground cover shall be planted one at one-foot-on-center and at the rate of one plant for every square foot of lot area of removed vegetation; and

(2)        Large trees shall be planted at the rate of one three-inch caliper tree for every 500 square feet of lot area of removed vegetation; or

(3)        Small trees shall be planted at a rate of one eight-foot high tree for every 100 square feet of lot area of removed vegetation; or

(4)        Shrubs shall be planted at a rate of one gallon container-grown material for every 25 square feet of lot area of removed vegetation.

The planting of species shall not be limited to woody plant materials, but shall include trees, shrubs, vines, ferns, grasses, herbs, annuals, biennials, perennials, mosses and other associated vegetation. All vegetation to be planted shall be either of the species which characterized the area's biological community prior to site alteration, enlargement or development, or of an alternative biologic community found in the area. Species selection shall give particular attention to the relationship of the species to each other and to the surrounding plant community and to the quality of the soil and the vertebrate and invertebrate populations associated with and dependent upon the proposed plants.