Tree Preservation Zone
ArboricultureA designated area around a tree, typically defined by the drip line, that is protected from construction activity to prevent root damage.
The Tree Preservation Zone (TPZ) is a defined area around a tree that must be protected during construction or development activities. It is typically calculated based on the tree's trunk diameter and species, often extending at least one foot of radius for every inch of trunk diameter at breast height. The TPZ aims to protect the critical root zone that the tree needs to survive.
Construction activities within the TPZ can cause irreversible damage through soil compaction, root severance, grade changes, and chemical contamination. Even driving heavy equipment over root zones can compact soil to the point where roots can no longer access oxygen and water. Damage may not become apparent for several years, leading to a delayed decline that is difficult to reverse.
Effective tree preservation requires planning before construction begins. Protective fencing should be installed at the TPZ boundary and maintained throughout the project. No storage of materials, parking of vehicles, or dumping of chemicals should occur within the zone. When encroachment is unavoidable, mitigation measures like root pruning, tunneling under roots for utilities, and soil decompaction can help minimize damage.