Under tree code adopted earlier this year, we've expanded what constitutes a "significant tree" that requires a permit for removal.  

None of the following trees may be removed without a permit:

• Oregon White Oak of 20 inches or greater in diameter at breast height (dbh)
• Other trees with a diameter at breast height of 30 inches or greater

Species excluded from the permit requirement are:

• Tree of heaven (Ailanthus altissima)
• Empress tree (Paulownia tomentosa)
• Black cottonwood (Populus trichocarpa)
• Black locust (Robinia pseudoacadia)

More details of new tree removal rules.