A tree higher climbs a tree that is imminent of being chopped down. Usually it's because the gov't wants a highway through that area or for commercial purposes. They want to chop down trees that are 300 years old fir the sake of development. The tree bugger stays in the tree to prevent it from happening. Go tree huggers!
Tree hugger is a term people use to describe people who care about the environment, which include plants and our planet and animals. This term originally emerged as a piece of derogatory slang, but it was later adopted by environmentalists to refer to them. This is an environmentalist, especially one concerned with preserving forests. For more details, visit http://www.wisegeek.com/what-is-a-tree-hugger.htm.