Lumber and engineered wood are materials derived from trees and include timber, lumber, veneer, wood pulp, wood flour, pellets and chips. There are two basic types of timber: hardwoods and softwoods. Hardwood trees have leaves, uneven branching patterns, and relatively long growing cycles. Examples include ash, beech, cherry, cypress, elm, hickory, maple, oak, and poplar trees. Softwood trees have needles and retain their foliage throughout the year. Examples include pine trees and fur trees. Timber from hardwoods such as white oak, black cherry, and red birch is more expensive than lumber and engineered wood made from softwoods. Higher-grade hardwoods have attractive grains and can be processed into veneer or lumber for furniture, cabinets, or flooring. Lower-grade hardwoods such as beech and hickory may check or split during drying. Lumber and engineered wood such as wood pulp are made from softwood trees such as spruce and pine. The production of wood pulp involves several steps. First, the bark is removed from the pulpwood tree. Next, the wood’s cellulose fibers are separated by chemical or mechanical methods to remove the lignin. Chemical pulps such as kraft pulp and sulfate pulp are created by combining wood chips with chemicals in vats or digesters. Mechanical pulps are produced by crushing the wood with grinders or refiners. Ground wood is pulp that is crushed and soaked in water. Thermomechanical pulp is crushed and heated with steam at high pressures and temperatures. Lumber and engineered wood such as recycle pulp are also commonly available. Although many companies still bleach wood pulp with chlorine, some pulp processing facilities use oxygen, ozone, or hydrogen peroxide instead. Wood and wood products include wood flour, wood pellets, and wood chips. Wood flour is a finely-pulverized wood product that is made from softwoods and used as a filler in thermosetting resins. Wood pellets are an extremely dense wood fuel made of compacted sawdust. Because they have a low humidity content, wood pellets burn with a relatively high combustion efficiency. Pellet stoves, wood stoves, and wood-burning furnaces can be used to heat residences, facilities, and other structures. Wood chips are made of green wood, pine needles, and leaves. They are sold in cubic yards and used in landscaping applications. Many other lumber and engienered wood products are also commonly available.