I learned that if you nail to a tree it will not kill it. No matter how large the nail. A tree only has a half on an inch that is alive. I always thought that you nail inot a tree it kills it. no matter the size. But a tree needs t obe bigger than 6" so it has enough strength to hold up what you are building. Using a rope to mount to a tree actually has causes more damage than oyu would think. it basically suffocates the tree. Another thing is if you use nails in a forest that will get cut, it is a hazard to the guys cutting, nails can cuase kick back. I guess many hippie activists would spike a whole forest to prevent cutting. If you all knew this already cool, i learned it today in my enviormental science class. My professor was the leader of greenpeace here in the Northwest, we had a chat today about trying to get more trails for us MTBers....hes actualy a good guy for being a greenpicer