……and to protect the tree. (protections from weather, insects and other animals, etc)

Bark can be used in products such as particleboard and fibreboard, and small amounts are tolerated in semichemical and kraft pulping processes. Bark also has utility as a source of adhesives and other chemicals (e.g., tannins, dyes, and waxes), in environmental protection applications (e.g., absorption of spilled oil, industrial wastes, and sewage effluents), and as a fuel. Nevertheless, differences in the structure and chemical composition of different barks, difficulties of separating bark from wood when in the form of particles, and differences in the properties of inner and outer bark have impeded fuller utilization.

Cork is also bark—the outer bark of a western Mediterranean oak, Quercus suber. It is stripped without adverse effects to the trees and grows again; it can be collected every 8–10 years. Aside from its use as bottle stoppers, cork is incorporated in life preservers and fishing equipment. As a reconstituted material (after chipping, grinding, and gluing), it finds uses as thermal and sound insulation, gaskets, flooring, bulletin boards, and various other products.