the Cali FS does have that rule. Even if you are a veteran feller or have tons of chainsaw experience (ie, enough to teach the fkin' class) you have to take their 2-day certification class just to help clear 4x4 trails.
Yes you do have to be certified to do VOLUNTEER work on trails using chainsaws or crosscut saws for that matter with the USFS. I think that's a good idea. A lot of people THINK they are experts and could teach the "fkin" class but they really aren't and couldn't. That's exactly why there is a certification process. It gets everybody on the same wavelength as far as safety goes. Safety is the most important aspect of the certification. They don't want folks who do stupid, unsafe things. We are not production cutters, we are volunteers who do what we can, and in a safe manner. We don't get as much done as a production cutter could, but what we do is better than nothing. We are not even supposed to be doing any falling. We are buckers.
The whole certification process was started after there was a series of falling accidents in the 1980s.
There is a difference between the classifications and the recertification requirements. The group I volunteer with is quite a large one and got the go ahead from the USFS to do their own certification. Instead of going through it every year, they go every other year and you are either an A bucker (trainee) or B bucker (good for any size). I've been B certified for chainsaw use and A certified for crosscut use. There's a lot to learn with the latter...
You also need to have a current First Aid and CPR card.