In the City of Portland a land division, property boundary line adjustment or the like will require a professional arborist to develop a tree preservation plan. All trees 6" in diameter and larger must be accounted for. There are various parameters based on the number of trees that are 20" diameter and larger, and requirements regarding the total inches of tree diameter on the property.

A Demolition Permit and a Development Permit both trigger additional obligations relating to street tree density and overall tree canopy area, based on the square footage of the property. In addition to 6" trees, there are obligations based on 12" trees, 20" trees, with special requirements for trees 36" and larger.