The burden of provision and selection of the buffer shall be as follows:
1. Where two different zoning districts, requiring a buffer between them, are both in an existing improved condition, the above requirement is not retroactive and should a buffer be desired, it shall be by mutual agreement between property owners or as otherwise provided by law. However, in the event of any or all of the improved property is abandoned, destroyed, demolished, etc., for the purpose of renewal or redevelopment, etc., that portion of such property being renewed or redeveloped, etc., shall be considered vacant land subject to the requirements herein.
2. Where one of two different zoning districts requiring a buffer between them is partially developed, the developer of the vacant land shall assume the burden, unless otherwise specified herein.
3. Where both zoning districts, requiring a buffer between them, are vacant or undeveloped, the burden shall be assumed by the developer of the more intense use.