The easiest way to find out if you need a permit for tree removal is to ask the local professionals about it.
I retired a few months ago and moved to Oahu. There are palms on my property that are more than 50 feet tall and that's too tall for me to trim myself. The arborist from the company I hired checked the trees and told me that one of the palms was dead and that it should be removed. I didn't get any permits for the removal, and they did it the same day. If anyone on Oahu Island needs the services of an arborist, I
used Oahu Tree Trimming.