north shore
If you know what your doing is going to kill the trees, why do it? You make all mountain bikers look like idiots to park rangers. If you need to put a beam elevated up in the air but against a tree, cut an upright log (dead or something you cart in) to the height you need, then metal strap that to the tree with nails (wont harm the tree) then put your beam on the top of your cut upright beam. The strapping will stop your upright from moving and the beam is supported by the upright you have cut. If your trail is on public land and your killing trees, and the wrong person finds it, it will either be wrecked and all your work is wasted or you may get in the shit from a ranger. Build your north shore dude, but do it smarter.