What do you mean by full benefits?? Many of the larger private tree services here offer medical, dental, 401k, paid holidays. Usually spouse, children cost extra though.
The union benefits are in a different league though. When I was line clearance I recieved $6000 yr. retirement without contributing anything(couldn't, didn't have a choice). Medical Dental was for whole family at no cost to employee(I believe they could have found better insurance for the 2.50hr the employer paid for it, but again, didn't have a choice) We didn't get paid holidays. The city of Portland climbers make great pay and get something like 6 weeks paid time off(holiday, vacation, sick) I can't remember the retirement details, but they're doing better than most private employees.
I checked those links Nick, and those are great examples of why a union is not needed.