The ultra-thin outer layer of bark peels during the spring revealing the smooth, cool silky-red new bark below. The rich, reddish coloration comes from tannins and other compounds manufactured by, and deposited in, the cells of the outer bark. Tannins are toxic to some organismsâ€”insects, birds, bacteria etc.â€”and most likely deter them from penetrating the stems and feeding on the tissue within. The peeling is thought to prevent fungi, parasites and epiphytesâ€”such as lichens and mossesâ€”from persisting on the tree's trunk and stems. Coupling the shedding bark and tannic compounds appears to discourage stem herbivory.