Wood surface, showing several features

Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers (which are strong in tension) embedded in a matrix of lignin which resists compression. Wood is sometimes defined as only the secondary xylem in the stems of trees,^[1] or it is defined more broadly to include the same type of tissue elsewhere such as in tree roots or in other plants such as shrubs.^{[citation needed]} In a living tree it performs a support function, enabling woody plants to grow large or to stand up for themselves. It also mediates the transfer of water and nutrients to the leaves and other growing tissues. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, or wood chips or fiber.

The earth contains about one trillion tonnes of wood, which grows at a rate of 10 billion tonnes per year. As an abundant, carbon-neutral renewable resource, woody materials have been of intense interest as a source of renewable energy. In 1991, approximately 3.5 billion cubic meters of wood were harvested. Dominant uses were for furniture and building construction.^[2]

History[link]

A 2011 discovery in the Canadian province of New Brunswick uncovered the earliest known plants to have grown wood, approximately 395 to 400 million years ago.^[3]

People have used wood for millennia for many purposes, primarily as a fuel or as a construction material for making houses, tools, weapons, furniture, packaging, artworks, and paper.

Wood can be dated by carbon dating and in some species by dendrochronology to make inferences about when a wooden object was created.

The year-to-year variation in tree-ring widths and isotopic abundances gives clues to the prevailing climate at that time.^[4]

Physical properties[link]

Growth rings[link]

Wood, in the strict sense, is yielded by trees, which increase in diameter by the formation, between the existing wood and the inner bark, of new woody layers which envelop the entire stem, living branches, and roots. This process is known as secondary growth; it is the result of cell division in the vascular cambium, a lateral meristem, and subsequent expansion of the new cells. Where there are clear seasons, growth can occur in a discrete annual or seasonal pattern, leading to growth rings; these can usually be most clearly seen on the end of a log, but are also visible on the other surfaces. If these seasons are annual these growth rings are referred to as annual rings. Where there is no seasonal difference growth rings are likely to be indistinct or absent.

If there are differences within a growth ring, then the part of a growth ring nearest the center of the tree, and formed early in the growing season when growth is rapid, is usually composed of wider elements. It is usually lighter in color than that near the outer portion of the ring, and is known as earlywood or springwood. The outer portion formed later in the season is then known as the latewood or summerwood.^[5] However, there are major differences, depending on the kind of wood (see below).

Knots[link]

A knot on a tree at the Garden of the Gods public park in Colorado Springs, Colorado (October 2006)

A knot is a particular type of imperfection in a piece of wood; it will affect the technical properties of the wood, usually for the worse, but may be exploited for visual effect. In a longitudinally sawn plank, a knot will appear as a roughly circular "solid" (usually darker) piece of wood around which the grain of the rest of the wood "flows" (parts and rejoins). Within a knot, the direction of the wood (grain direction) is up to 90 degrees different from the grain direction of the regular wood.

In the tree a knot is either the base of a side branch or a dormant bud. A knot (when the base of a side branch) is conical in shape (hence the roughly circular cross-section) with the inner tip at the point in stem diameter at which the plant's vascular cambium was located when the branch formed as a bud.

During the development of a tree, the lower limbs often die, but may remain attached for a time, sometimes years. Subsequent layers of growth of the attaching stem are no longer intimately joined with the dead limb, but are grown around it. Hence, dead branches produce knots which are not attached, and likely to drop out after the tree has been sawn into boards.

In grading lumber and structural timber, knots are classified according to their form, size, soundness, and the firmness with which they are held in place. This firmness is affected by, among other factors, the length of time for which the branch was dead while the attaching stem continued to grow.

Wood Knot

Knots materially affect cracking and warping, ease in working, and cleavability of timber. They are defects which weaken timber and lower its value for structural purposes where strength is an important consideration. The weakening effect is much more serious when timber is subjected to forces perpendicular to the grain and/or tension than where under load along the grain and/or compression. The extent to which knots affect the strength of a beam depends upon their position, size, number, and condition. A knot on the upper side is compressed, while one on the lower side is subjected to tension. If there is a season check in the knot, as is often the case, it will offer little resistance to this tensile stress. Small knots, however, may be located along the neutral plane of a beam and increase the strength by preventing longitudinal shearing. Knots in a board or plank are least injurious when they extend through it at right angles to its broadest surface. Knots which occur near the ends of a beam do not weaken it. Sound knots which occur in the central portion one-fourth the height of the beam from either edge are not serious defects.^[6]

Knots do not necessarily influence the stiffness of structural timber, this will depend on the size and location. Stiffness and elastic strength are more dependent upon the sound wood than upon localized defects. The breaking strength is very susceptible to defects. Sound knots do not weaken wood when subject to compression parallel to the grain.

In some decorative applications, wood with knots may be desirable to add visual interest. In applications where wood is painted, such as skirting boards, fascia boards, door frames and furniture, resins present in the timber may continue to 'bleed' through to the surface of a knot for months or even years after manufacture and show as a yellow or brownish stain. A knot primer paint or solution, correctly applied during preparation, may do much to reduce this problem but it is difficult to control completely, especially when using mass-produced kiln-dried timber stocks.

Heartwood and sapwood[link]

A section of a Yew branch showing 27 annual growth rings, pale sapwood and dark heartwood, and pith (centre dark spot). The dark radial lines are small knots.

Heartwood (or duramen^[7]) is wood that as a result of a naturally occurring chemical transformation has become more resistant to decay. Heartwood formation occurs spontaneously (it is a genetically programmed process). Once heartwood formation is complete, the heartwood is dead.^[8] Some uncertainty still exists as to whether heartwood is truly dead, as it can still chemically react to decay organisms, but only once.^[9]

Usually heartwood looks different; in that case it can be seen on a cross-section, usually following the growth rings in shape. Heartwood may (or may not) be much darker than living wood. It may (or may not) be sharply distinct from the sapwood. However, other processes, such as decay, can discolor wood, even in woody plants that do not form heartwood, with a similar color difference, which may lead to confusion.

Sapwood (or alburnum^[7]) is the younger, outermost wood; in the growing tree it is living wood,^[8] and its principal functions are to conduct water from the roots to the leaves and to store up and give back according to the season the reserves prepared in the leaves. However, by the time they become competent to conduct water, all xylem tracheids and vessels have lost their cytoplasm and the cells are therefore functionally dead. All wood in a tree is first formed as sapwood. The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests. Sometimes trees (of species that do form heartwood) grown in the open may become of considerable size, 30 cm or more in diameter, before any heartwood begins to form, for example, in second-growth hickory, or open-grown pines.

The term heartwood derives solely from its position and not from any vital importance to the tree. This is evidenced by the fact that a tree can thrive with its heart completely decayed. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut, black locust, mulberry, osage-orange, and sassafras, while in maple, ash, hickory, hackberry, beech, and pine, thick sapwood is the rule. Others never form heartwood.

No definite relation exists between the annual rings of growth and the amount of sapwood. Within the same species the cross-sectional area of the sapwood is very roughly proportional to the size of the crown of the tree. If the rings are narrow, more of them are required than where they are wide. As the tree gets larger, the sapwood must necessarily become thinner or increase materially in volume. Sapwood is thicker in the upper portion of the trunk of a tree than near the base, because the age and the diameter of the upper sections are less.

When a tree is very young it is covered with limbs almost, if not entirely, to the ground, but as it grows older some or all of them will eventually die and are either broken off or fall off. Subsequent growth of wood may completely conceal the stubs which will however remain as knots. No matter how smooth and clear a log is on the outside, it is more or less knotty near the middle. Consequently the sapwood of an old tree, and particularly of a forest-grown tree, will be freer from knots than the inner heartwood. Since in most uses of wood, knots are defects that weaken the timber and interfere with its ease of working and other properties, it follows that a given piece of sapwood, because of its position in the tree, may well be stronger than a piece of heartwood from the same tree.

It is remarkable that the inner heartwood of old trees remains as sound as it usually does, since in many cases it is hundreds, and in a few instances thousands, of years old. Every broken limb or root, or deep wound from fire, insects, or falling timber, may afford an entrance for decay, which, once started, may penetrate to all parts of the trunk. The larvae of many insects bore into the trees and their tunnels remain indefinitely as sources of weakness. Whatever advantages, however, that sapwood may have in this connection are due solely to its relative age and position.

If a tree grows all its life in the open and the conditions of soil and site remain unchanged, it will make its most rapid growth in youth, and gradually decline. The annual rings of growth are for many years quite wide, but later they become narrower and narrower. Since each succeeding ring is laid down on the outside of the wood previously formed, it follows that unless a tree materially increases its production of wood from year to year, the rings must necessarily become thinner as the trunk gets wider. As a tree reaches maturity its crown becomes more open and the annual wood production is lessened, thereby reducing still more the width of the growth rings. In the case of forest-grown trees so much depends upon the competition of the trees in their struggle for light and nourishment that periods of rapid and slow growth may alternate. Some trees, such as southern oaks, maintain the same width of ring for hundreds of years. Upon the whole, however, as a tree gets larger in diameter the width of the growth rings decreases.

Different pieces of wood cut from a large tree may differ decidedly, particularly if the tree is big and mature. In some trees, the wood laid on late in the life of a tree is softer, lighter, weaker, and more even-textured than that produced earlier, but in other trees, the reverse applies. This may or may not correspond to heartwood and sapwood. In a large log the sapwood, because of the time in the life of the tree when it was grown, may be inferior in hardness, strength, and toughness to equally sound heartwood from the same log. In a smaller tree, the reverse may be true.

Color[link]

In species which show a distinct difference between heartwood and sapwood the natural color of heartwood is usually darker than that of the sapwood, and very frequently the contrast is conspicuous (see section of yew log above). This is produced by deposits in the heartwood of chemical substances, so that a dramatic color difference does not mean a dramatic difference in the mechanical properties of heartwood and sapwood, although there may be a dramatic chemical difference.

Some experiments on very resinous Longleaf Pine specimens indicate an increase in strength, due to the resin which increases the strength when dry. Such resin-saturated heartwood is called "fat lighter". Structures built of fat lighter are almost impervious to rot and termites; however they are very flammable. Stumps of old longleaf pines are often dug, split into small pieces and sold as kindling for fires. Stumps thus dug may actually remain a century or more since being cut. Spruce impregnated with crude resin and dried is also greatly increased in strength thereby.

The wood of Coast Redwood is distinctively red in color

Since the latewood of a growth ring is usually darker in color than the earlywood, this fact may be used in judging the density, and therefore the hardness and strength of the material. This is particularly the case with coniferous woods. In ring-porous woods the vessels of the early wood not infrequently appear on a finished surface as darker than the denser latewood, though on cross sections of heartwood the reverse is commonly true. Except in the manner just stated the color of wood is no indication of strength.

Abnormal discoloration of wood often denotes a diseased condition, indicating unsoundness. The black check in western hemlock is the result of insect attacks. The reddish-brown streaks so common in hickory and certain other woods are mostly the result of injury by birds. The discoloration is merely an indication of an injury, and in all probability does not of itself affect the properties of the wood. Certain rot-producing fungi impart to wood characteristic colors which thus become symptomatic of weakness; however an attractive effect known as spalting produced by this process is often considered a desirable characteristic. Ordinary sap-staining is due to fungal growth, but does not necessarily produce a weakening effect.

Water content[link]

Water occurs in living wood in three conditions, namely: (1) in the cell walls, (2) in the protoplasmic contents of the cells, and (3) as free water in the cell cavities and spaces. In heartwood it occurs only in the first and last forms. Wood that is thoroughly air-dried retains 8–16% of the water in the cell walls, and none, or practically none, in the other forms. Even oven-dried wood retains a small percentage of moisture, but for all except chemical purposes, may be considered absolutely dry.

The general effect of the water content upon the wood substance is to render it softer and more pliable. A similar effect of common observation is in the softening action of water on paper or cloth. Within certain limits, the greater the water content, the greater its softening effect.

Drying produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry spruce block 5 cm in section, which will sustain a permanent load four times as great as a green (undried) block of the same size will.^{[citation needed]}

The greatest strength increase due to drying is in the ultimate crushing strength, and strength at elastic limit in endwise compression; these are followed by the modulus of rupture, and stress at elastic limit in cross-bending, while the modulus of elasticity is least affected.

Structure[link]

Wood is a heterogeneous, hygroscopic, cellular and anisotropic material. It is composed of cells, and the cell walls are composed of micro-fibrils of cellulose (40% – 50%) and hemicellulose (15% – 25%) impregnated with lignin (15% – 30%).^[10]

Sections of tree trunk

A tree trunk as found at the Veluwe, Netherlands

In coniferous or softwood species the wood cells are mostly of one kind, tracheids, and as a result the material is much more uniform in structure than that of most hardwoods. There are no vessels ("pores") in coniferous wood such as one sees so prominently in oak and ash, for example.

The structure of hardwoods is more complex.^[11] The water conducting capability is mostly taken care of by vessels: in some cases (oak, chestnut, ash) these are quite large and distinct, in others (buckeye, poplar, willow) too small to be seen without a hand lens. In discussing such woods it is customary to divide them into two large classes, ring-porous and diffuse-porous. In ring-porous species, such as ash, black locust, catalpa, chestnut, elm, hickory, mulberry, and oak, the larger vessels or pores (as cross sections of vessels are called) are localised in the part of the growth ring formed in spring, thus forming a region of more or less open and porous tissue. The rest of the ring, produced in summer, is made up of smaller vessels and a much greater proportion of wood fibers. These fiber are the elements which give strength and toughness to wood, while the vessels are a source of weakness.

Magnified cross-section of Black Walnut, showing the vessels, rays (white lines) and annual rings: this is intermediate between diffuse-porous and ring-porous, with vessel size declining gradually

In diffuse-porous woods the pores are evenly sized so that the water conducting capability is scattered throughout the growth ring instead of being collected in a band or row. Examples of this kind of wood are basswood, birch, buckeye, maple, poplar, and willow. Some species, such as walnut and cherry, are on the border between the two classes, forming an intermediate group.

Earlywood and latewood in softwood[link]

earlywood and latewood in a softwood; radial view, growth rings closely spaced in a Pseudotsuga taxifolia

In temperate softwoods there often is a marked difference between latewood and earlywood. The latewood will be denser than that formed early in the season. When examined under a microscope the cells of dense latewood are seen to be very thick-walled and with very small cell cavities, while those formed first in the season have thin walls and large cell cavities. The strength is in the walls, not the cavities. Hence the greater the proportion of latewood the greater the density and strength. In choosing a piece of pine where strength or stiffness is the important consideration, the principal thing to observe is the comparative amounts of earlywood and latewood. The width of ring is not nearly so important as the proportion and nature of the latewood in the ring.

If a heavy piece of pine is compared with a lightweight piece it will be seen at once that the heavier one contains a larger proportion of latewood than the other, and is therefore showing more clearly demarcated growth rings. In white pines there is not much contrast between the different parts of the ring, and as a result the wood is very uniform in texture and is easy to work. In hard pines, on the other hand, the latewood is very dense and is deep-colored, presenting a very decided contrast to the soft, straw-colored earlywood.

It is not only the proportion of latewood, but also its quality, that counts. In specimens that show a very large proportion of latewood it may be noticeably more porous and weigh considerably less than the latewood in pieces that contain but little. One can judge comparative density, and therefore to some extent strength, by visual inspection.

No satisfactory explanation can as yet be given for the exact mechanisms determining the formation of earlywood and latewood. Several factors may be involved. In conifers, at least, rate of growth alone does not determine the proportion of the two portions of the ring, for in some cases the wood of slow growth is very hard and heavy, while in others the opposite is true. The quality of the site where the tree grows undoubtedly affects the character of the wood formed, though it is not possible to formulate a rule governing it. In general, however, it may be said that where strength or ease of working is essential, woods of moderate to slow growth should be chosen.

Earlywood and latewood in ring-porous woods[link]

Earlywood and latewood in a ring-porous wood (ash) in a Fraxinus excelsior ; tangential view, wide growth rings

In ring-porous woods each season's growth is always well defined, because the large pores formed early in the season abut on the denser tissue of the year before.

In the case of the ring-porous hardwoods there seems to exist a pretty definite relation between the rate of growth of timber and its properties. This may be briefly summed up in the general statement that the more rapid the growth or the wider the rings of growth, the heavier, harder, stronger, and stiffer the wood. This, it must be remembered, applies only to ring-porous woods such as oak, ash, hickory, and others of the same group, and is, of course, subject to some exceptions and limitations.

In ring-porous woods of good growth it is usually the latewood in which the thick-walled, strength-giving fibers are most abundant. As the breadth of ring diminishes, this latewood is reduced so that very slow growth produces comparatively light, porous wood composed of thin-walled vessels and wood parenchyma. In good oak these large vessels of the earlywood occupy from 6 to 10 percent of the volume of the log, while in inferior material they may make up 25% or more. The latewood of good oak is dark colored and firm, and consists mostly of thick-walled fibers which form one-half or more of the wood. In inferior oak, this latewood is much reduced both in quantity and quality. Such variation is very largely the result of rate of growth.

Wide-ringed wood is often called "second-growth", because the growth of the young timber in open stands after the old trees have been removed is more rapid than in trees in a closed forest, and in the manufacture of articles where strength is an important consideration such "second-growth" hardwood material is preferred. This is particularly the case in the choice of hickory for handles and spokes. Here not only strength, but toughness and resilience are important. The results of a series of tests on hickory by the U.S. Forest Service show that:

"The work or shock-resisting ability is greatest in wide-ringed wood that has from 5 to 14 rings per inch (rings 1.8-5 mm thick), is fairly constant from 14 to 38 rings per inch (rings 0.7–1.8 mm thick), and decreases rapidly from 38 to 47 rings per inch (rings 0.5–0.7 mm thick). The strength at maximum load is not so great with the most rapid-growing wood; it is maximum with from 14 to 20 rings per inch (rings 1.3–1.8 mm thick), and again becomes less as the wood becomes more closely ringed. The natural deduction is that wood of first-class mechanical value shows from 5 to 20 rings per inch (rings 1.3–5 mm thick) and that slower growth yields poorer stock. Thus the inspector or buyer of hickory should discriminate against timber that has more than 20 rings per inch (rings less than 1.3 mm thick). Exceptions exist, however, in the case of normal growth upon dry situations, in which the slow-growing material may be strong and tough."^[12]

The effect of rate of growth on the qualities of chestnut wood is summarised by the same authority as follows:

"When the rings are wide, the transition from spring wood to summer wood is gradual, while in the narrow rings the spring wood passes into summer wood abruptly. The width of the spring wood changes but little with the width of the annual ring, so that the narrowing or broadening of the annual ring is always at the expense of the summer wood. The narrow vessels of the summer wood make it richer in wood substance than the spring wood composed of wide vessels. Therefore, rapid-growing specimens with wide rings have more wood substance than slow-growing trees with narrow rings. Since the more the wood substance the greater the weight, and the greater the weight the stronger the wood, chestnuts with wide rings must have stronger wood than chestnuts with narrow rings. This agrees with the accepted view that sprouts (which always have wide rings) yield better and stronger wood than seedling chestnuts, which grow more slowly in diameter."^[12]

Earlywood and latewood in diffuse-porous woods[link]

In the diffuse-porous woods, the demarcation between rings is not always so clear and in some cases is almost (if not entirely) invisible to the unaided eye. Conversely, when there is a clear demarcation there may not be a noticeable difference in structure within the growth ring.

In diffuse-porous woods, as has been stated, the vessels or pores are even-sized, so that the water conducting capability is scattered throughout the ring instead of collected in the earlywood. The effect of rate of growth is, therefore, not the same as in the ring-porous woods, approaching more nearly the conditions in the conifers. In general it may be stated that such woods of medium growth afford stronger material than when very rapidly or very slowly grown. In many uses of wood, total strength is not the main consideration. If ease of working is prized, wood should be chosen with regard to its uniformity of texture and straightness of grain, which will in most cases occur when there is little contrast between the latewood of one season's growth and the earlywood of the next.

Monocot wood[link]

Trunks of the Coconut palm, a monocot, in Java. From this perspective these look not much different from trunks of a dicot or conifer

Structural material that roughly (in its gross handling characteristics) resembles ordinary, "dicot" or conifer wood is produced by a number of monocot plants, and these also are colloquially called wood. Of these, bamboo, botanically a member of the grass family, has considerable economic importance, larger culms being widely used as a building and construction material in their own right and, these days, in the manufacture of engineered flooring, panels and veneer. Another major plant group that produce material that often is called wood are the palms. Of much less importance are plants such as Pandanus, Dracaena and Cordyline. With all this material, the structure and composition of the structural material is quite different from ordinary wood.

Hard and soft woods[link]

There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it. The density of wood varies with species. The density of a wood correlates with its strength (mechanical properties). For example, mahogany is a medium-dense hardwood that is excellent for fine furniture crafting, whereas balsa is light, making it useful for model building. One of the densest woods is black ironwood.

It is common to classify wood as either softwood or hardwood. The wood from conifers (e.g. pine) is called softwood, and the wood from dicotyledons (usually broad-leaved trees, e.g. oak) is called hardwood. These names are a bit misleading, as hardwoods are not necessarily hard, and softwoods are not necessarily soft. The well-known balsa (a hardwood) is actually softer than any commercial softwood. Conversely, some softwoods (e.g. yew) are harder than many hardwoods.

Chemistry of wood[link]

Aside from water, wood has three main components. Cellulose, a crystalline polymer derived from glucose, constitutes about 41–43%. Next in abundance is hemicellulose, which is around 20% in deciduous trees but near 30% in conifers. It is mainly five-carbon sugars that are linked in an irregular manner, in contrast to the cellulose. Lignin is the third component at around 27% in coniferous wood vs 23% in deciduous trees. Lignin confers the hydrophobic properties reflecting the fact that it is based on aromatic rings. These three components are interwoven, and direct covalent linkages exist between the lignin and the hemicellulose. A major focus of the paper industry is the separation of the lignin from the cellulose, from which paper is made.

Chemical structure of lignin, which comprises approximately 30% of wood and is responsible for many of its properties.

In chemical terms, the difference between hardwood and softwood is reflected in the composition of the constituent lignin. Hardwood lignin is primarily derived from sinapyl alcohol and coniferyl alcohol. Softwood lignin is mainly derived from coniferyl alcohol.^[13]

Extractives[link]

Aside from the lignocellulose, wood consists of a variety of low molecular weight organic compounds, called extractives. The wood extractives are fatty acids, resin acids, waxes and terpenes.^[14] For example, rosin is exuded by conifers as protection from insects. The extraction of these organic materials from wood provides tall oil, terpentine, and rosin.^[15]

Uses[link]

Fuel[link]

Wood has a long history of being used as fuel, which continues to this day, mostly in rural areas of the world. Hardwood is preferred over softwood because it creates less smoke and burns longer. Adding a woodstove or fireplace to a home is often felt to add ambiance and warmth.^[16]

The churches of Kizhi, Russia are among a handful of World Heritage Sites built entirely of wood, without metal joints. See Kizhi Pogost for more details.

The complex carpentry of the Centre Pompidou-Metz museum, Metz.

Construction[link]

Wood has been an important construction material since humans began building shelters, houses and boats. Nearly all boats were made out of wood until the late 19th century, and wood remains in common use today in boat construction.

Wood to be used for construction work is commonly known as lumber in North America. Elsewhere, lumber usually refers to felled trees, and the word for sawn planks ready for use is timber.

New domestic housing in many parts of the world today is commonly made from timber-framed construction. Engineered wood products are becoming a bigger part of the construction industry. They may be used in both residential and commercial buildings as structural and aesthetic materials.

In buildings made of other materials, wood will still be found as a supporting material, especially in roof construction, in interior doors and their frames, and as exterior cladding.

Wood is also commonly used as shuttering material to form the mould into which concrete is poured during reinforced concrete construction.

Furniture and utensils[link]

Wood has always been used extensively for furniture, such as chairs and beds. Also for tool handles and cutlery, such as chopsticks, toothpicks, and other utensils, like the wooden spoon.

Engineered wood[link]

Wood can be cut into straight planks and made into a wood flooring.

Engineered wood products, glued building products "engineered" for application-specific performance requirements, are often used in construction and industrial applications. Glued engineered wood products are manufactured by bonding together wood strands, veneers, lumber or other forms of wood fiber with glue to form a larger, more efficient composite structural unit.^[18] These products include glued laminated timber (glulam), wood structural panels (including plywood, oriented strand board and composite panels), laminated veneer lumber (LVL) and other structural composite lumber (SCL) products, parallel strand lumber, and I-joists.^[18] Approximately 100 million cubic meters of wood was consumed for this purpose in 1991.^[2] The trends suggest that particle board and fiber board will overtake plywood.

Engineered wood products display highly predictable and reliable performance characteristics and provide enhanced design flexibility: on one hand, these products allow the use of smaller pieces, and on the other hand, they allow for bigger spans. They may also be selected for specific projects such as public swimming pools or ice rinks where the wood will not deteriorate in the presence of certain chemicals, and are less susceptible to the humidity changes commonly found in these environments.

Engineered wood products prove to be more environmentally friendly and, if used appropriately, are often less expensive than building materials such as steel or concrete. These products are extremely resource-efficient because they use more of the available resource with minimal waste. In most cases, engineered wood products are produced using faster growing and often underutilized wood species from managed forests and tree farms.^[19]

Wood unsuitable for construction in its native form may be broken down mechanically (into fibers or chips) or chemically (into cellulose) and used as a raw material for other building materials, such as engineered wood, as well as chipboard, hardboard, and medium-density fiberboard (MDF). Such wood derivatives are widely used: wood fibers are an important component of most paper, and cellulose is used as a component of some synthetic materials. Wood derivatives can also be used for kinds of flooring, for example laminate flooring.

Next generation wood products[link]

Further developments include new lignin glue applications, recyclable food packaging, rubber tire replacement applications, anti-bacterial medical agents, and high strength fabrics or composites.^[20] As scientists and engineers further learn and develop new techniques to extract various components from wood, or alternatively to modify wood, for example by adding components to wood, new more advanced products will appear on the marketplace.

In the arts[link]

Artists can use wood to create delicate sculptures.

Stringed instrument bows are often made from pernambuco or brazilwood.

Wood has long been used as an artistic medium. It has been used to make sculptures and carvings for millennia. Examples include the totem poles carved by North American indigenous people from conifer trunks, often Western Red Cedar (Thuja plicata), and the Millennium clock tower,^[21] now housed in the National Museum of Scotland^[22] in Edinburgh.

It is also used in woodcut printmaking, and for engraving.

Certain types of musical instruments, such as those of the violin family, the guitar, the clarinet and recorder, the xylophone, and the marimba, are made mostly or entirely of wood. The choice of wood may make a significant difference to the tone and resonant qualities of the instrument, and tonewoods have widely differing properties, ranging from the hard and dense african blackwood (used for the bodies of clarinets) to the light but resonant European spruce (Picea abies) (traditionally used for the soundboards of violins). The most valuable tonewoods, such as the ripple sycamore (Acer pseudoplatanus), used for the backs of violins, combine acoustic properties with decorative color and grain which enhance the appearance of the finished instrument.

Despite their collective name, not all woodwind instruments are made entirely of wood. The reeds used to play them, however, are usually made from Arundo donax, a type of monocot cane plant.

Sports and recreational equipment[link]

Many types of sports equipment are made of wood, or were constructed of wood in the past. For example, cricket bats are typically made of white willow. The baseball bats which are legal for use in Major League Baseball are frequently made of ash wood or hickory, and in recent years have been constructed from maple even though that wood is somewhat more fragile. In softball, however, bats are more commonly made of aluminium (this is especially true for fastpitch softball).

Many other types of sports and recreation equipment, such as skis, ice hockey sticks, lacrosse sticks and archery bows, were commonly made of wood in the past, but have since been replaced with more modern materials such as aluminium, fiberglass, carbon fiber, titanium, and composite materials. One noteworthy example of this trend is the golf club commonly known as the wood, the head of which was traditionally made of persimmon wood in the early days of the game of golf, but is now generally made of synthetic materials.

Medicine[link]

In January 2010 Italian scientists announced that wood could be harnessed to become a bone substitute. It is likely to take at least five years until this technique will be applied for humans.^[23]

See also[link]

Notes[link]

References[link]

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Eva Marie Cassidy (February 2, 1963 – November 2, 1996) was an American vocalist known for her interpretations of jazz, blues, folk, gospel, country and pop classics. In 1992 she released her first album, The Other Side, a set of duets with go-go musician Chuck Brown, followed by a live solo album, Live at Blues Alley in 1996. Although she had been honored by the Washington Area Music Association, she was virtually unknown outside her native Washington, D.C., when she died of melanoma (skin cancer) in 1996.

Four years later, Cassidy's music was brought to the attention of British audiences when her version of "Over the Rainbow" was played by Terry Wogan on BBC Radio 2. Following the overwhelming response, a camcorder recording of "Over the Rainbow", taken at Blues Alley in Washington, was shown on BBC Two's Top of the Pops 2. Shortly afterwards, the compilation album Songbird climbed to the top of the UK Albums Charts, almost three years after its initial release. The chart success in the United Kingdom and Ireland led to increased recognition worldwide; her posthumously released recordings, including three UK number 1s, have sold more than ten million copies.^[1] Her music has also charted top 10 positions in Australia, Germany, Sweden, Norway and Switzerland.^[2]

Biography[link]

Early life[link]

Born on February 2, 1963, at the Washington Hospital Center,^[3] Cassidy grew up in Oxon Hill and later Bowie, Maryland, suburbs of Washington, D.C.. She was the third of four children born to Hugh and Barbara Cassidy. Her father, a retired teacher, sculptor, musician, Powerlifter and former army medic, is of Scottish and Irish descent, while her German-born mother was a horticulturist.^[2][4][5] From an early age, Cassidy displayed interest in art and music. When she was nine, her father taught her to play the guitar and she began to play and sing at family gatherings.^[4]

At age 11, Cassidy began singing and playing guitar in a Washington area band called Easy Street.^[6] This band performed in a variety of styles at weddings, corporate parties and pubs. Due to her shyness, she struggled with performing in front of strangers. While a student at Bowie High School, she sang with a local band called Stonehenge.^[4] During the summer of 1983, Cassidy sang and played guitar six days a week at the theme park Wild World.^[4] Her younger brother Dan, a fiddler, was also a member of this working band. She enrolled in art classes at a community college but dropped out after finding them unhelpful.^[7]

Throughout the 1980s, Cassidy worked with several other bands, including the techno-pop band Characters Without Names. During this period, Cassidy also worked as a propagator at a plant nursery and as a furniture painter. In her free time, she explored other artistic expressions including painting, sculpting and jewelry design.^[7] Despite holding a belief in God, Cassidy was not part of any organized religion.^[8]

Music career[link]

In 1986, Cassidy was asked by Stonehenge guitarist and high school friend, David Lourim, to lend her voice to his music project, Method Actor.^[9] This brought her to Black Pond Studios, where she met bassist and recording engineer Chris Biondo. Biondo helped her find work as a session singer and later introduced her to Al Dale, who would become her manager. She sang back-ups for various acts, from go-go rhythm and blues band Experience Unlimited to rapper E-40.^[10] Biondo and Cassidy, who were in a romantic relationship for a time, formed the five-piece "Eva Cassidy Band" with Lenny Williams, Keith Grimes and Raice McLeod in 1990. They began to perform frequently in the Washington area.^[4]

	"Over the Rainbow" noicon One of the changes Cassidy made to "Over the Rainbow" includes singing the opening word "somewhere" on the same high A flat, rather than with an octave jump of the Judy Garland version.
Problems listening to this file? See media help.

	"Stormy Monday" noicon Cassidy's arrangement of T-Bone Walker's popular blues song.
Problems listening to this file? See media help.

In 1992, Biondo played a tape of Cassidy's voice for Chuck Brown, the "Godfather of go-go".^[11] It resulted in the duet album The Other Side featuring performances of classic songs such as "Fever", "God Bless the Child," and what would later become Cassidy's signature song, "Over the Rainbow". The album was released and distributed in 1992 by Liaison Records, the label that also released Brown's Go-go albums. Brown originally intended to record a single duet with Cassidy for his next solo album, but this was postponed due to ongoing negotiations between Dale and other labels for a solo deal.^[10][12] Cassidy's unwillingness to narrow her stylistic focus to one genre hindered her chances of securing a deal.^[13][14] After talks broke down, the two decided to record their own duet album. As a duo, they performed at the Columbia Arts Festival and opened for acts like Al Green and The Neville Brothers.^[10]

In 1993, Cassidy was honored by the Washington Area Music Association with a Wammie award for the Vocalist Jazz/Traditional category.^[15] The next year she was invited to perform at the event and chose to sing "Over the Rainbow". A Washington Times review of the event called her performance "a show-stopper".^[16] She took home two Wammies that night, again for Vocalist Jazz/Traditional and also for Roots Rock/Traditional R&B.^[15] For a brief period that year, Cassidy signed a deal with Blue Note Records to pair up with pop-jazz band Pieces of a Dream to release an album and tour the country. She sang two tracks in a mainly instrumental album. It was a musically unsatisfying experience for her.^[10]

After having a potential contract with Apollo Records collapse when the label went bankrupt, Biondo and Dale decided that she should release her own live album.^[10] In January 1996, the material for Live at Blues Alley was recorded over a two-day period at Blues Alley, Washington, D.C. Due to a technical glitch on the first night of recording,^[17] only the second night's recording was usable. Unhappy with the way she sounded due to a cold, she was reluctant to release the album. She eventually relented, on the condition that the studio track "Oh, Had I a Golden Thread", Cassidy's favorite song,^[18] would be included in the release, and that they start working on a follow-up studio album.^[7][10] Her apprehension appeared unfounded as local reviewers and the public responded positively.^[7] The Washington Post commented that "she could sing anything — folk, blues, pop, jazz, R&B, gospel — and make it sound like it was the only music that mattered."^[11] The subsequent studio album she worked on was released as Eva by Heart posthumously in 1997. In the liner notes of Eva by Heart, critic Joel E. Siegel described Cassidy as "one of the greatest voices of her generation."^[7]

Death[link]

In 1993, Cassidy had a malignant mole removed from her back. Three years later, during a promotional event for the Live at Blues Alley album in July 1996, Cassidy noticed an ache in her hips, which she attributed to stiffness from painting murals while perched atop a stepladder.^[11] The pain persisted and a few weeks later, X-rays revealed that the melanoma had spread to her lungs and bones. Her doctors estimated she had three to five months to live. Cassidy opted for aggressive treatment, but her health deteriorated rapidly. In the early fall, at a benefit concert for her at the Bayou, she made her final public appearance, closing the set with "What a Wonderful World" in front of an audience of friends, fans and family. Additional chemotherapy was uneffective, and within six weeks she had died.^[2][11][19]

Cassidy died on November 2, 1996, at her family home in Bowie, Maryland. She was 33. In accordance with her wishes, her body was cremated and the ashes were scattered on the lake shores of St. Mary's River Watershed Park, a nature reserve near Callaway, Maryland.^[2]

Posthumous recognition[link]

After Cassidy's death, local folk singer Grace Griffith introduced the Blues Alley recording to Bill Straw from her label, Blix Street Records.^[19] Straw approached the Cassidy family to put together a new album. In 1998, a compilation of tracks from Cassidy's three released recordings was assembled into the CD Songbird. This CD lingered in relative obscurity for two years until being given airplay by Terry Wogan on his wide-reaching BBC Radio 2 show Wake Up to Wogan, following recommendation by his producer Paul Walters. The album sold more than 100,000 copies in the following months.^[2] The New York Times spoke of her "silken soprano voice with a wide and seemingly effortless range, unerring pitch and a gift for phrasing that at times was heart-stoppingly eloquent."^[19]

Before Christmas of 2000, Top Of The Pops 2 aired a video of Cassidy performing "Over the Rainbow", which resulted in Songbird climbing steadily up the UK charts over the next few weeks. Just as ITV's Tonight with Trevor McDonald aired a feature on Cassidy, the album topped the chart.^[20] Shot at Blues Alley by a friend with a camcorder the same night the album was recorded,^[2] the video became the most requested video ever shown on Top Of The Pops 2.^[21] "There's an undeniable emotional appeal in hearing an artist who you know died in obscurity singing a song about hope and a mystical world beyond everyday life", wrote The Guardian.^[22]

Paul McCartney and Eric Clapton were among her new-found fans. Jazz critic Ted Gioia writes, "you might be tempted to write off the 'Cassidy sensation' [...] as a response to the sad story of the singer's abbreviated life rather than as a measure of her artistry. But don't be mistaken, Cassidy was a huge talent, whose obscurity during her lifetime was almost as much a tragedy as her early death."^[23] Songbird has since achieved significant chart success throughout Europe and six times platinum status in the UK.^[2][24] Although still relatively unknown in the United States at that time, the album would eventually be certified gold in the U.S. as well.^[25]

In May 2001, ABC's Nightline in the United States broadcast a well-received short documentary about Cassidy.^[26] Over the weekend, all five of Cassidy's albums occupied Amazon.com's best sellers list top spots.^[27] The Nightline episode has since been rebroadcast three times due to popular demand.^[28] Producer Leroy Sievers has said that it is "probably the most popular Nightline ever".^[29] In December, a nine-minute segment on NPR resulted in a similar sales surge, with five of the top seven spots going to Cassidy.^[4] A rebroadcast of the Tonight with Trevor McDonald feature on Cassidy in Britain also bumped up sales.^[4][30]

Since Songbird, several other CDs with original material have been released: Time After Time (2000), Imagine (2002) and American Tune (2003). 2008 saw the release of another new album titled Somewhere. Unlike previous albums, which consisted solely of cover songs, this release contains two original songs co-written by Cassidy. An acoustic album titled Simply Eva was released in January 2011.

Together with word of mouth and internet fansites, online commerce has played a big role in Cassidy's success.^[31][32] This point was further affirmed when in 2005, Amazon.com released a list of its top 25 best-selling musicians, which placed Cassidy in fifth position, behind The Beatles, U2, Norah Jones and Diana Krall,^[33] and far ahead of Elvis Presley and several other well-known stars.^[34]

In 2004, during the gala opening of the Bowie Center for the Performing Arts, the Bowie Regional Arts Vision Association, Inc. (BRAVA) dedicated the Star's Dressing Room to Eva. Following a moving tribute to Eva, Chuck Brown took the stage and performed his duet "with" Eva as her photos and video appeared in the background.

Unofficial recordings[link]

A collection of previously unreleased studio recordings from 1987 to 1991, was released in 2000 as No Boundaries. This release was not endorsed by the Cassidy family^[2] and was released under a different label. An allmusic review of the album stated that even "a gifted vocalist like Eva Cassidy can only do so much with bad material".^[35] In 2002, the self titled 1988 album by the band Method Actor, which featured Cassidy, was re-released by the band's guitarist and producer David Lourim with Cassidy's name displayed prominently on the cover. The Cassidy family and Blix Street Records filed a lawsuit against Lourim, claiming that Cassidy's name was used in a misleading fashion and that Blix Street has exclusive rights to her recordings.^[36] Lourim had Cassidy's written permission to release the album and eventually the cover was changed to look like the original LP album while already released copies were affixed with a sticker indicating that they are not solo Eva Cassidy albums.^[37][38]

A bootleg recording which has been in circulation is called Live at Pearl's. It was recorded at Pearl's Restaurant in Annapolis, Maryland in 1994. Copies of the recording were circulated among friends and families after her death. Some of the songs on the recording are also on Imagine and American Tune.^[39] Another recording, featuring Mick Fleetwood on drums and recorded at his restaurant in Alexandria, Virginia called Fleetwood's in the early 1990s, was in the possession of Niki Lee - the former wife of pianist Lenny Williams - who discovered it in her garage and attempted to sell it on eBay in 2008.^[40]

In popular media[link]

In 2001, a book titled Songbird: Eva Cassidy: Her Story By Those Who Knew Her, on the life and work of Cassidy based on interviews with close family and associates was released in the UK. The hardcover edition has since sold in excess of 100,000 copies. A U.S. edition published by Gotham Books was released in late 2003 and includes two additional chapters on her influences and success in the US. Her life story has also been adapted into a musical^[41] and also a Broadway piece for cancer benefit.^[42]

At the 2002 Winter Olympics gala, and later on tour, figure skater Michelle Kwan brought Cassidy's music to a new audience when she skated to a recording of "Fields of Gold". Kwan's part in exposing the music of Cassidy to the international and American public led Cassidy's label to present her a gold record from the certification of Songbird.^[43] Subsequently, other figure skaters such as Kristi Yamaguchi, Sarah Hughes and Kimmie Meissner have used Cassidy's music in their routines.

Anglo-Georgian singer Katie Melua is a keen fan of Cassidy.^[44] Her debut album "Call Off the Search" contained the song "Faraway Voice", written in Cassidy's memory.^[44] Melua has also performed Cassidy's arrangement of "Anniversary Song" in concert.^[44] On Christmas Eve 2006, she performed alongside video footage of Cassidy singing Over The Rainbow on BBC One's "Duet Impossible".^[45] One year later, Cassidy's "What A Wonderful World" was spliced together with new vocals by Melua and released as a single exclusively at the British retail chain Tesco. It debuted at #1 on the UK Singles chart on December 16. All profits from the single went to the British Red Cross.^[46] Irish singer Chris de Burgh has stated that his song "Songbird" from his album The Road to Freedom was written in honour of Cassidy. Singer Mary Chapin Carpenter made reference to Cassidy in the song "My Heaven" on the album Between Here and Gone: "More memories than my heart can hold, when Eva's singing 'Fields of Gold'."

In 2008, Cassidy's recording of "Autumn Leaves" was used by the Canadian National Professional Latin Champions, Andre and Natalie Paramonov, when they competed in America's Ballroom Challenge as finalists in the International Latin Competition.

The first film to feature an Eva Cassidy recording was Flight of Fancy starring Dean Cain. Since then her music has appeared in various film and TV series including the Dawson's Creek season four episode titled "The Graduate," Judging Amy, Joe Somebody, Love Actually, Maid in Manhattan, The Man From Elysian Fields, Alpha Dog and Smallville. Cassidy's arrangement of "Over the Rainbow" is a popular cover choice by singing competition contestants, with American Idol season 5 runner-up Katharine McPhee and The X Factor season 3 winner Leona Lewis among the singers. Her interpretation of "Imagine" has been performed by American Idol season 7 runner-up David Archuleta.

In March 2012, Sweden's Caroline Larsson and Bengt Magnusson released an album entitled A Tribute to Eva Cassidy.

Possibility of future film[link]

In late 2007, AIR Productions acquired the rights to produce a film based on Cassidy's life.^[47] It is being produced by Amy Redford (daughter of Robert Redford), Irwin Shapiro and Rick Singer.^[48] In an interview a year earlier, Cassidy's parents suggested Kirsten Dunst or Emily Watson as possible actresses who could play their daughter.^[49]

A documentary on the life, art and music of Cassidy entitled Eva's Song is expected to be in theaters February 2013.^[50]

Discography[link]

Albums[link]

Singles[link]

Bootleg[link]

Videography[link]

References[link]

Notes[link]

Books[link]

• Rob Burley; Jonathan Maitland, Elana Rhodes Byrd (2003). Eva Cassidy: Songbird: Her Story by Those Who Knew Her. Gotham Books. ISBN 978-1-59240-035-5. 
• Johan Bakker; Behind the Rainbow, the tragic life of Eva Cassidy (2012) Omnibus Press, 207 pages, ISBN 978-1-78038-231-9

External links[link]

• Eva Cassidy website maintained by her cousin, Laura Claire Bligh
• Eva Cassidy Artwork website
• Evasongs recordings information
• Eva Cassidy at the All Music Guide
• Eva Cassidy on ABC Nightline
• Eva Cassidy Feature on ABC Nightline
• Eva Cassidy: Songbird: Her Story by Those Who Knew Her at Google Book Search
• Over the Rainbow on YouTube – Eva plays live, recorded on a friend's video camera — became the most requested video ever shown on Top Of The Pops 2.
• Tears in Heaven on YouTube - Mary Ann Redmond & Eva Cassidy singing Eric Clapton's "Tears in Heaven" – From a 1995 performance at Fleetwood's in Alexandria, VA.
• Website Eva Cassidy Biography