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Portland Trees

Call before you cut

phone: (503) 823-TREE (8733)


1900 SW 4th Avenue, Portland, OR 97201

Prescriptive Path

root protection zoneThe Prescriptive Path method of tree protection establishes a root protection zone (see diagram at right) and blocks this zone from construction activities. The prescriptive path calls for the root protection zone to have a 1-foot radius from the center of the trunk per inch of tree diameter. For example, a 12-inch diameter tree would require a 12-foot radius root protection zone.

The root protection fencing must be a minimum of 6-foot high chain link fence secured with 8-foot metal posts, at the edge of the root protection zone. Place the yellow sign marked ‘Tree Root Protection Zone’ prominently on the fence designating the root protection zone and describing the penalties for violation. Install the fence before any ground-disturbing activities take place, including clearing, grading, or construction. Keep the fence in place until final inspection.

Encroachments in the root protection zone

Construction activities may encroach on no more than 25% of the root protection zone area. The encroachment may not be closer than one half of the root protection zone radius.

Prohibited activities in the root protection zone

Some construction activities are prohibited in any part of the root protection zone. These activities include:

  • ground disturbance
  • construction activity involving vehicle or equipment access (unless the access is on an existing street or driveway)
  • storage of equipment or materials (including soil)
  • temporary or permanent stockpiling
  • proposed buildings
  • impervious surfaces
  • underground utilities
  • excavation or fill
  • trenching
  • other work activities

Root cutting

Cutting a large percentage of a tree’s roots can be dangerous. Most large tree roots, those over 4 inches in diameter, are structural roots that support the tree. If large roots are disturbed or removed, the tree may fall over and/or decline or die. Roots over 4 inches in diameter should not be cut.  If cutting a tree’s roots is unavoidable, a certified arborist must approve and oversee the root cutting.