A private protected tree has a trunk 44"+ in circumference (14" diameter) at 54". You need a permit to remove one or to prune it excessively. Denials can be appealed to the Beautification Commission.
How to apply: Submit a Private Protected Tree Removal Permit application to the Burlingame City Arborist. An independent arborist report may be requested.
How to measure: most Bay Area cities measure trunk diameter (or circumference) at 4.5 ft (54") above natural grade, but some measure elsewhere: Berkeley at 4 ft, Redwood City at the widest point between 6" and 36". Where a city sets its limit by circumference, we show the diameter (circumference ÷ 3.14).
Official sources: burlingame.org/472/Private-Protected-Tree-FAQ