lol
same dilemma I had 11 years ago...lived with my grandparents, who had two mimosa trees in the front yard.
assuming they're the right species, the root bark is what's used. taking the outer parts of the root bark will not kill the tree, it regenerates.
"Nothing is true, everything is permitted." ~ hassan i sabbah
"Experiments are the only means of attaining knowledge at our disposal. The rest is poetry, imagination." -Max Planck