If you want the rules, here's the rules. It is, of course, every individuals choice to follow these rules or not...
Pisgah District: Every trail in the district is assigned to a volunteer group. According to the FS, no group or individual is allowed to work on a trail without this assignment, although exceptions can be made with coordination with the district. This does NOT include simple corridor clearing- in other words, if you just move a rock out of the trail, that's fine. Any work outside of the existing trail (such as removing a tree) not only has to be done by the assigned group, the FS has to receive notification of the action. Use of herbicides would require a full assessment regarding possible groundwater, habitat, etc impact -not likely. All trailworkers have to wear a helmet or hard hat, work gloves, and closed toe shoes. Also, they will not give any individual or group credit for a work without being reported, so any "bandit" work by MTB'ers never happened in their eyes and MTB'ers continue to have the mislabel of not being involved. Plus, anybody hurt doing trailwork not part of a sanctioned effort will not be covered by the FS insurance, although they will be if part of a sanctioned volunteer group. These are all reasons why it's so important to be part of the group effort...wait, wait, I got to get off the soapbox....
Grandfather District: Has a less formal Adopt-a-Trail program. Any group or individual can request a trail if it is not already assigned. Through the program, a sign will be posted giving the group or individual credit for the trail work. The group or individual agrees to at least three (spring, summer, fall) corridor maintenance days as well as being available for "emergency" maintenance such as the removal of downed trees. This is much less formal than the Pisgah District volunteer agreements. FWIW, the individual who does the ORAMM is in the process of adopting HeartBreak Ridge/Star Gap and another area group is considering adopting Kitsuma, although that trail is so blown-out that the group is a bit worried about the size of the work which needs to be done. Again, trail work beyond simple clearing of debris and obstacles is not supposed to occur outside of this program, but Grandfather District appears to be much less formally managed...
It's a federal bureaucracy- the rules are nightmarish and are implemented differently in each district. I happen to work in a different cog of the vast government machine, so I'm pretty used to having to deal with ridiculous rules...but still, these are pretty amazing in their ridiculousness.
Individuals interested in becoming involved in these efforts should, of course, join Pisgah Area SORBA.
Peace,
Mike