Wood
**History and Traditional Uses of Wood:**
– Wood has been used for various purposes such as fuel, construction, tools, weapons, furniture, and paper for thousands of years.
– Its use in constructions like Neolithic longhouses and recent enhancements with steel and bronze in construction.
– Tree-ring widths and isotopic abundances provide insights into past climates.
**Physical Properties of Wood:**
– Wood is yielded by trees through secondary growth, with growth rings showing annual or seasonal patterns.
– Different parts of a growth ring are formed by earlywood and latewood, influenced by tree growth conditions.
– Competition among forest trees affects growth ring width.
**Wood Growth and Structure:**
– Wood is a heterogeneous material composed of cells with cell walls made of cellulose, hemicellulose, and lignin.
– Coniferous wood mainly consists of tracheids without vessels, while hardwoods have a more complex structure with vessels for water conduction.
– Hardwoods are categorized into ring-porous and diffuse-porous classes based on vessel distribution.
**Growth Rings and Vessel Distribution:**
– Wide-ringed wood, termed second-growth, is preferred for strength-related applications.
– Ring-porous woods have well-defined growth rings with a relation between growth rate and wood properties.
– Vessel distribution in woods like ash and oak affects strength and texture, while walnut and cherry woods show intermediate characteristics.
**Heartwood, Sapwood, Color, and Water Content:**
– Heartwood is more resistant to decay and visually distinct from sapwood, with heartwood formation being a genetically programmed process.
– Color variations in wood do not necessarily indicate mechanical differences, and abnormal discoloration may signal disease or weakness.
– Water content affects wood softness and pliability, with different properties between heartwood and sapwood.
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Wood is a structural tissue found in the stems and roots of trees and other woody plants. It is an organic material – a natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin that resists compression. Wood is sometimes defined as only the secondary xylem in the stems of trees, or more broadly to include the same type of tissue elsewhere, such as in the roots of trees or shrubs. In a living tree it performs a support function, enabling woody plants to grow large or to stand up by themselves. It also conveys water and nutrients between the leaves, other growing tissues, and the roots. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, woodchips, or fiber.
Wood samples
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Wood has been used for thousands of years for fuel, as a construction material, for making tools and weapons, furniture and paper. More recently it emerged as a feedstock for the production of purified cellulose and its derivatives, such as cellophane and cellulose acetate.
As of 2020, the growing stock of forests worldwide was about 557 billion cubic meters. As an abundant, carbon-neutral renewable resource, woody materials have been of intense interest as a source of renewable energy. In 2008, approximately 3.97 billion cubic meters of wood were harvested. Dominant uses were for furniture and building construction.