high angle rescue
if anyone is truly serious about rescues involving scenarios arborists might find themselves in a high angle rescue class is great. i had to take a high angle class in college that focused on everything from anchor systems to belay escapes to climber pick-offs. everything was rock climbing oriented, but easily translates to any other profession that involves working at heights.
there are great ways to access an incapacitated person at heights and safely lower them, they usually take more to learn than an internet chat room can offer however. there are some great books on the subject and you'd be amazed at what you don't know about rigging once you read some of them.
searches for high angle rescue or tower rescue classes and books are a great start.