Guidelines for Arborist Reports

Find out when you need an arborist report when you're building or renovating. Learn more about what an arborist report must include. Get information about tree reports from arborists before development begins. And, find out what you need from an arborist after work has started.
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An arborist report may be required of applicants for projects:

  • As part of a land division application
  • This might be when the Prescriptive Tree Protection method is not practical.
  • When revisions or changes to tree protection are proposed after development has started, as per 11.60.030. 

Reports must be submitted by an arborist, as defined in chapter 11.80.020.B.3:

“A professional listed as a certified arborist by the International Society of Arboriculture [ISA] or a consulting arborist registered with the American Society of Consulting Arborists [ASCA].”

You can find a certified arborist on the International Society of Arboriculture (ISA) website and the American Society of Consulting Arborists website.

Report Includes Information About the Arborist and the Last Assessment 

The arborist report must include:

  1. Arborist Information
    • ISA or ASCA number
    • Contact information
    • Name and signature
  2. Date and time of most recent assessment
  3. Tree Species, Tolerance and Previous Impacts to Trees
    • Tree information to include:
      1. Specify the tree’s species (taxonomic ID), size (DBH), condition, location, and extent of root cover
      2. Describe the tree’s tolerance to construction impact based on its species and health
      3. Identify any prior impacts that have occurred within the root zone
  4. How and why proposed protection measures allow for continued tree preservation
  5. A site plan that follows requirements as per 11.50.070 and demonstrates how the protection plan conforms to the site and the proposed development activity. 
  6. Include supporting documents and photographs with your report

Before Development Begins 

If development has not started (see Performance Path Tree Protection Plans 11.60.030.C.2):

  • Explanation of why the Prescriptive Path (11.60.030.C.1) is not practicable
  • Detailed description of alternate tree protection measures, including remedial actions taken to mitigate negative impacts on the tree, if necessary
  • Description of alternate construction techniques and materials, if applicable 
  • If tree protection measures need an arborist to be onsite:
    • Provide stages of construction arborist is to be onsite
    • Copy of the contract for onsite inspections and final report
    • Final arborist report verifying the viability of tree(s) provided before final inspection

After Development Has Started 

If construction has started and corrections are needed:

  • Description of how the tree has been impacted by the onsite development activity
  • Explanation of techniques and materials used to ensure continued viability of tree to be preserved 
  • Description of the proposed tree protection measures to be implemented

Questions About Arborist Reports 

For more information regarding City of Portland Title 11, contact the Urban Forestry phone number.

Read the Tree Code, Title 11