The cork oak is the main tree species used to produce natural cork for bottle stoppers.
Its thick, spongy bark can be harvested without killing the tree. The outer bark is carefully stripped from the trunk and large branches, then allowed to regrow. A cork oak usually needs to mature for roughly 20 years before its first harvest, while later harvests can be made at intervals of several years.
Cork production is strongly associated with the western Mediterranean, especially Portugal and Spain, as well as parts of North Africa, Italy and France. Portugal is the leading cork-producing country.
Cork oak is an evergreen oak, so it keeps its leaves through winter. It is sometimes confused with corkwood trees, but corkwood is a different group of plants whose lightweight wood—not harvestable bark—is the notable feature.