We used one when we were there. I think it is ok as long as you are not damaging the tree.
I certainly don't see why not. If you're camping with a hammock just be sure to follow rules related to camping, distance from trail, distance from water, etc.
I have not seen or heard that they were not allowed either way. However the safe bet is to call or ask a ranger to be on the safe side.
Just use a sturdy trees
As far as I know
I'm not sure please ask a ranger.
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