I do understand the desire to study and work with trees, but why not use a non-destructive means of establishing a relationship to a tree species? Would you intentionally do harm to an animal that you're studying, just to establish a relationship with it? Trees may not bleed, but removing branches can leave the tree open to disease and insect damage. Just saying...
I understand and do sympathesize with your point, but I really don't believe that cutting one small branch off a mature tree will do it harm. Pruning and cutting back of plants is a common practice. Trees lose branches to wind and animals with out ill effects. I don't really see a problem with cutting the branch as a negative impact to the tree. But I do kind of see the taking of the branch as a selfish act...
The idea is to wander around in the woods until I find a tree that is willing to communicate and give up a branch. But your posts have made me realize that I can pick up a branch from the ground, and separately, find a tree that calls to me to communicate/work with it.