Once fertilized, a female flower will become an acorn. The acorn is the fruit of the oak. Oaks grow slowly and usually do not bear acorns until they are about 20 years old. But these trees live a long time. Most oaks live for 200 to 400 years.
Oaks are an important source of lumber.
Oak wood is heavy, hard, and strong, and it has a beautiful grain. Manufacturers use it for furniture, barrels, and railroad ties. The wood and bark of some oaks contain tannin, a bitter substance used in the preparation of leather. Cork comes from the bark of certain oaks. Acorns are an important source of food for wildlife.