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{{short description|Fibrous material from trees or other plants}}
{{otheruses}}
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'''Wood''' is hard, fibrous, ] structural tissue produced as secondary ] in the stems of ]s, notably trees but also shrubs. In a living tree it conducts water and nutrients to the leaves and other growing tissues, and has a support function, enabling plants to reach large sizes. Wood may also refer to other plant materials and tissues with comparable properties.
{{for-multi|a small forest|Woodland|wood as a commodity|Timber|other uses|Wood (disambiguation)|and|Wooden (disambiguation)}}
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{{Use American English|date=October 2012}}<!--THIS ARTICLE WAS STARTED IN AMERICAN SPELLING. PLEASE KEEP PER WP:ENGVAR-->
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]s can use wood to create delicate ]s.]]
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People have used wood for millennia for many purposes, primarily as a ] material, for making ]s, ]s, ] and artworks and as a ]. Wood can be ] to make inferences about when a wooden object was created and the climate at that time.
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==Formation==
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A tree increases in ] by the formation, between the old wood and the inner ], of new woody layers which envelop the entire stem, living branches, and roots. Where there are clear seasons, this can happen in a discrete pattern, leading to what is known as ], as can be seen from a viewpoint perpendicular to the surface of a radial cut of a wood specimen, a specimen of a wood species which necessary have growth rings, of which some do not. If these seasons are annual these growth rings are annual rings. Where there is no seasonal difference growth rings are likely to be indistinct or absent.
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'''Wood''' is a structural tissue/material found as '']'' in the ] and roots of ]s and other ]s. It is an ]{{snd}}a natural ] of ] fibers that are strong in tension and embedded in a ] of ] that resists compression. Wood is sometimes defined as only the secondary ] in the stems of trees,<ref>{{cite book|author=Hickey, M.|author2=King, C.|date=2001|title=The Cambridge Illustrated Glossary of Botanical Terms|publisher=Cambridge University Press}}</ref> 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 mechanical-support function, enabling woody plants to grow large or to stand up by themselves. It also conveys water and ]s among the ], other growing tissues, and the roots. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, ], or ]s.

Wood has been used for thousands of years for ], as a ], for making ]s and ]s, ] and ]. More recently it emerged as a feedstock for the production of purified cellulose and its derivatives, such as ] and ].

As of 2020, the growing stock of ]s worldwide was about 557 billion cubic meters.<ref name="FAO-2020">FAO. 2020. '' {{Webarchive|url=https://web.archive.org/web/20221105155828/https://www.fao.org/3/ca9825en/ca9825en.pdf |date=November 5, 2022 }}.'' Rome.</ref> As an abundant, ]<ref>{{cite web | url=https://www.smithsonianmag.com/smart-news/epa-declares-burning-wood-carbon-neutral-180968880/ | title=The EPA Declared That Burning Wood is Carbon Neutral. It's Actually a Lot More Complicated | access-date=June 3, 2022 | archive-date=June 30, 2021 | archive-url=https://web.archive.org/web/20210630153427/https://www.smithsonianmag.com/smart-news/epa-declares-burning-wood-carbon-neutral-180968880/ | url-status=live }}</ref> 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.<ref name="FAO-2020" /> Dominant uses were for furniture and building construction.<ref name="Horst-2005">Horst H. Nimz, Uwe Schmitt, Eckart Schwab, Otto Wittmann, Franz Wolf "Wood" in ''Ullmann's Encyclopedia of Industrial Chemistry'' 2005, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a28_305}}</ref>

Wood is scientifically studied and researched through the discipline of ], which was initiated since the beginning of the 20th century.

==History==

A 2011 discovery in the ] of ] yielded the earliest known plants to have grown wood, approximately 395 to 400 ].<ref>{{cite news|url=https://www.cbc.ca/news/canada/new-brunswick/n-b-fossils-show-origins-of-wood-1.1052870|title=N.B. fossils show origins of wood|publisher=]|access-date=August 12, 2011|date=August 12, 2011|url-status=live|archive-url=https://web.archive.org/web/20110813012432/http://www.cbc.ca/news/canada/new-brunswick/story/2011/08/12/nb-origins-of-wood-found.html|archive-date=August 13, 2011|df=mdy-all}}</ref><ref>{{cite journal|last1=Philippe Gerrienne|display-authors=etal|title=A Simple Type of Wood in Two Early Devonian Plants|journal=Science|volume=333|issue=6044|pages=837|date=Aug 12, 2011|doi=10.1126/science.1208882|pmid=21836008|bibcode=2011Sci...333..837G|hdl=2268/97121 |s2cid=23513139|url=http://orbi.ulg.ac.be/jspui/handle/2268/97121|hdl-access=free}}{{Dead link|date=October 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Wood can be dated by ] and in some species by ] to determine when a wooden object was created.

People have used wood for thousands of years for many purposes, including as a ] or as a ] material for making ]s, ]s, ]s, ], ], ]s, and ]. Known ]s using wood date back ten thousand years. Buildings like the longhouses in ] Europe were made primarily of wood.

Recent use of wood has been enhanced by the addition of steel and bronze into construction.<ref name="Woods-2017">{{cite web|last1=Woods|first1=Sarah|title=A History of Wood from the Stone Age to the 21st Century|url=http://www.ecobuildingpulse.com/products/a-history-of-wood_o|website=EcoBUILDING|publisher=A Publication of The American Institute of Architects|access-date=March 28, 2017|ref=3|url-status=live|archive-url=https://web.archive.org/web/20170329051421/http://www.ecobuildingpulse.com/products/a-history-of-wood_o|archive-date=March 29, 2017|df=mdy-all}}</ref>

The year-to-year variation in tree-ring widths and isotopic abundances gives ] to the prevailing climate at the time a tree was cut.<ref name="Briffa-2008" >{{cite journal
|author=Briffa, K.
|date=2008
|title=Trends in recent temperature and radial tree growth spanning 2000 years across northwest Eurasia
|journal=Philosophical Transactions of the Royal Society B: Biological Sciences
|issue= 1501
|pages=2271–2284
|doi=10.1098/rstb.2007.2199
|pmid=18048299
|volume=363
|pmc=2606779
|last2=Shishov
|first2=V.V.
|last3=Melvin
|first3=T.M.
|last4=Vaganov
|first4=E.A.
|last5=Grudd
|first5=H.
|last6=Hantemirov}}</ref>

==Physical properties==
] in a ] showing idealized vertical and horizontal sections. A new layer of wood is added in each growing season, thickening the stem, existing branches and ]s, to form a ].]]

===Growth rings===
{{see also|Dendrochronology#Growth rings}}

Wood, in the strict sense, is yielded by ]s, which increase in ] by the formation, between the existing wood and the inner ], of new woody layers which envelop the entire stem, living branches, and roots. This process is known as ]; it is the result of cell division in the ], a lateral meristem, and subsequent expansion of the new cells. These cells then go on to form thickened secondary cell walls, composed mainly of ], ] and ].

Where the differences between the seasons are distinct, e.g. ], growth can occur in a discrete annual or seasonal pattern, leading to ]s; these can usually be most clearly seen on the end of a log, but are also visible on the other surfaces. If the distinctiveness between seasons is annual (as is the case in equatorial regions, e.g. ]), these growth rings are referred to as annual rings. Where there is little seasonal difference growth rings are likely to be indistinct or absent. If the bark of the tree has been removed in a particular area, the rings will likely be deformed as the plant overgrows the scar.


Within a growth ring, the observer is in a situation which permits the possibility of the observance of two parts. The part nearest the centre of the tree is more open ]d and almost invariably lighter in colour than that near the outer portion of the ring. The inner portion is formed early in the season, when growth is comparatively rapid; it is known as early wood or spring wood. The outer portion is the late wood or summer wood, being produced in the summer.<ref> www.farmforestline.com.au</ref> In ]s there is not much contrast in the different parts of the ring, and as a result the wood is very uniform in texture and is easy to work. In ], on the other hand, the late wood is very dense and is deep-coloured, presenting a very decided contrast to the soft, straw-coloured early wood. In ring-porous woods each season's growth is always well defined, because the large pores of the spring abut on the denser tissue of the fall before. 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. 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.<ref> {{webarchive|url=https://web.archive.org/web/20091212121121/http://farmforestline.com.au/pages/2.1.2.1_wood.html |date=December 12, 2009 }} www.farmforestline.com.au</ref> There are major differences, depending on the kind of wood. If a tree grows all its life in the open and the conditions of ] 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 ]s, maintain the same width of ring for hundreds of years. On the whole, as a tree gets larger in diameter the width of the growth rings decreases.


===Knots=== ===Knots===
<!--] and ] redirect directly here.-->
] public park in ], ] (October 2006).]]
]
A knot is a particular type of imperfection in a piece of timber, which reduces its strength, but which may be exploited for artistic effect. In a longitudinally-sawn plank, a knot will appear as a roughly circular "solid" (usually darker) piece of wood around which the roughly parallel fibres (]) of the rest of the "flows" (parts and rejoins).


As a tree grows, lower branches often die, and their bases may become overgrown and enclosed by subsequent layers of trunk wood, forming a type of imperfection known as a knot. The dead branch may not be attached to the trunk wood except at its base and can drop out after the tree has been sawn into boards. Knots affect the technical properties of the wood, usually reducing tension strength,<ref>{{cite book |last1=Everett |first1=Alan |last2=Barritt |first2=C. M. H. |title=Materials |date=12 May 2014 |publisher=Routledge |isbn=978-1-317-89327-1 |page=38 |url=https://books.google.com/books?id=ncCOAwAAQBAJ&pg=PT38 |language=en |access-date=March 20, 2023 |archive-date=September 8, 2023 |archive-url=https://web.archive.org/web/20230908234050/https://books.google.com/books?id=ncCOAwAAQBAJ&pg=PT38 |url-status=live }} "Knots, particularly edge and arris knots, reduce strength mainly in tension, but not in resistance to shear and splitting."</ref> 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 ] 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.
A knot is actually a portion of a side ] (or a dormant bud) included in the wood of the stem or larger branch. The included portion is irregularly conical in shape (hence the roughly circular cross-section) with the tip at the point in stem diameter at which the plant's ] was located when the branch formed as a bud. Within a knot, the fibre direction (grain) is up to 90 degrees different from the fibres of the stem, thus producing local cross grain.


In the tree a knot is either the base of a side ] 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 persist 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. In grading ] and structural ], 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.


]
Knots materially affect cracking (known in the industry as checking) 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 ] than where under load along the grain and/or ]. The extent to which knots affect the strength of a ] depends upon their position, size, number, direction of ], 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 ]. 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.
{{blockquote|''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 ] than when under load along the grain and/or ]. The extent to which knots affect the strength of a ] 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 may be located along the neutral plane of a beam and increase the strength by preventing longitudinal ]. 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.''|Samuel J. Record|The Mechanical Properties of Wood<ref name="Record-1914">{{cite book
|last = Record
|first = Samuel J
|title = The Mechanical Properties of Wood
|publisher = J. Wiley & Sons
|year = 1914
|page = 165
|url = https://www.gutenberg.org/ebooks/12299
|asin = B000863N3W
|asin-tld = co.uk
|access-date = August 28, 2020
|archive-date = October 18, 2020
|archive-url = https://web.archive.org/web/20201018011708/http://www.gutenberg.org/ebooks/12299
|url-status = live
}}</ref>}}


Knots do not necessarily influence the stiffness of structural timber. Only defects of the most serious character affect the elastic limit of beams. Stiffness and elastic strength are more dependent upon the quality of the wood fibre than upon defects in the beam. The effect of knots is to reduce the difference between the fibre stress at elastic limit and the ] of rupture of beams. The breaking strength is very susceptible to defects. Sound knots do not weaken wood when subject to compression parallel to the grain. 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 ], 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 ] paint or solution (knotting), 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.
For purposes that favour appearance over strength, such as wall panelling, knots are considered a benefit as they add visual texture to the wood and gives it a more interesting appearance.


===Heartwood and sapwood===<!-- ] and ] redirect here -->
The traditional style of playing the Basque xylophon '']'' involves hitting the right knots to obtain different tones.
{{Redirect|Heartwood}}
{{Redirect|Sapwood|the missile also called "SS-6 Sapwood"|R7 Semyorka}}
{{see also|Trunk (botany)}}
] branch showing 27 annual growth rings, pale sapwood, dark heartwood, and ] (center dark spot). The dark radial lines are small knots.]]
'''Heartwood''' (or duramen<ref name="Britannica-1911">{{Cite EB1911|wstitle=Duramen|volume=8|page=692|short=y}}</ref>) is wood that as a result of a naturally occurring chemical transformation has become more resistant to decay. Heartwood formation is a genetically programmed process that occurs spontaneously. Some uncertainty exists as to whether the wood dies during heartwood formation, as it can still chemically react to decay organisms, but only once.<ref>Shigo, Alex. (1986) ''A New Tree Biology Dictionary''. Shigo and Trees, Associates. {{ISBN|0-943563-12-7}}</ref>


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 ], ], ], ], and ], while in ], ], ], ], ], and pine, thick sapwood is the rule.<ref>{{Cite book|url=https://archive.org/details/mechanicalprope02recogoog|page=|quote=The term heartwood derives solely from its position and not from any vital importance to the tree as a tree can thrive with heart completely decayed.|title=The Mechanical Properties of Wood: Including a Discussion of the Factors Affecting the Mechanical Properties, and Methods of Timber Testing|last=Record|first=Samuel James|date=1914|publisher=J. Wiley & Sons, Incorporated|language=en|df=mdy-all}}</ref> Some others never form heartwood.
===Heartwood and sapwood===<!-- This section is linked from ] -->
] branch showing 27 annual growth rings, pale sapwood and dark heartwood, and ] (centre dark spot). The dark radial lines are small knots.]]
Heartwood is wood that has died and become resistant to decay as a result of genetically programmed processes. It appears in a cross-section as a discoloured circle, following annual rings in shape. Heartwood is usually much darker than living wood, and forms with age. Many woody plants do not form heartwood, but other processes, such as decay, can discoulor wood in similar ways, leading to confusion. Some uncertainty still exists as to whether heartwood is truly dead, as it can still chemically react to decay organisms, but only once (Shigo 1986, 54).


Heartwood is often visually distinct from the living sapwood and can be distinguished in a cross-section where the boundary will tend to follow the growth rings. For example, it is sometimes much darker. Other processes such as decay or insect invasion can also discolor wood, even in woody plants that do not form heartwood, which may lead to confusion.
Sapwood is living wood in the growing tree. All wood in a tree is first formed as sapwood. Its principal functions are to conduct water from the ]s to the ] and to store up and give back according to the season the food prepared in the leaves. 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 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 ], or open-grown ]s.


'''Sapwood''' (or alburnum<ref name="Alburnum-1911">{{Cite EB1911|wstitle=Alburnum|volume=1|page=516|short=y}}</ref>) is the younger, outermost wood; in the growing tree it is living wood,<ref>Capon, Brian (2005), Botany for Gardeners (2nd ed.), Portland, OR: Timber Publishing, p. 65 {{ISBN|0-88192-655-8}}</ref> and its principal functions are to conduct water from the ]s to the ] and to store up and give back according to the season the reserves prepared in the leaves. 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, {{convert|30|cm|abbr=on}} or more in diameter, before any heartwood begins to form, for example, in second growth ], or open-grown ]s.
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 and have only a thin layer of live sapwood, while for other species the change comes slowly. Thin sapwood is characteristic of such trees as ], ], ], ], and ], while in ], ], hickory, ], ], and pine, thick sapwood is the rule.
]


There is no definite relation 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. 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 relatively 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 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 sapwood, because of its position in the tree, may have certain advantages over heartwood. 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 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.


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 ], ], and toughness to equally sound heartwood from the same log. In a smaller tree, the reverse may be true.
It is remarkable that the inner heartwood of old trees remains as sound as it usually does, since in many cases it is hundreds of years, 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.


===Color===
If a tree grows all its life in the open and the conditions of ] 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 ]s, 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.
] is distinctively red.]]
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 variation does not imply a significant difference in the mechanical properties of heartwood and sapwood, although there may be a marked biochemical difference between the two.


Some experiments on very resinous ] specimens indicate an increase in strength, due to the ] 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 ]s, and very flammable. ]s 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. ] impregnated with crude resin and dried is also greatly increased in strength thereby.
There may be decided differences in the grain of heartwood and sapwood cut from a large tree, particularly one that is 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 species, the reverse applies. In a large log the sapwood, because of the time in the life of the tree when it was grown, may be inferior in ], ], and toughness to equally sound heartwood from the same log.


Since the latewood of a growth ring is usually darker in color than the earlywood, this fact may be used in visually 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 often appear on a finished surface as darker than the denser latewood, though on cross sections of heartwood the reverse is commonly true. Otherwise the color of wood is no indication of strength.
==Different woods==
There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it. For every tree species there is a range of density for the wood it yields. There is a rough correlation between density of a wood and its strength (mechanical properties). For example, while ] is a medium-dense hardwood which is excellent for fine furniture crafting, ] is light, making it useful for ] building. The densest wood may be ].


Abnormal discoloration of wood often denotes a diseased condition, indicating unsoundness. The black check in western ] 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 ] impart to wood characteristic colors which thus become symptomatic of weakness. Ordinary sap-staining is due to fungal growth, but does not necessarily produce a weakening effect.
Wood is commonly classified as either ] or hardwood. The wood from ] (e.g. pine) is called softwood, and the wood from ] (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. ]) are harder than most hardwoods.


===Water content===
Wood products such as ] are typically classified as engineered wood and not considered raw wood.
Water occurs in living wood in three locations, namely:
* in the ]s
* in the ]ic contents of the ]
* as free water in the cell cavities and spaces, especially of the xylem
]
In heartwood it occurs only in the first and last forms. Wood that is thoroughly air-dried (in ] with the moisture content of the air) 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 ] upon the wood substance is to render it softer and more pliable. A similar effect occurs in the softening action of water on rawhide, paper, or cloth. Within certain limits, the greater the water content, the greater its softening effect. The moisture in wood can be measured by several different ]s.
===Colour===
In species which show a distinct difference between heartwood and sapwood the natural colour of heartwood is usually darker than that of the sapwood, and very frequently the contrast is conspicuous. This is produced by deposits in the heartwood of various materials resulting from the process of growth, increased possibly by ] and other chemical changes, which usually have little or no appreciable effect on the mechanical properties of the wood. Some experiments on very resinous ] specimens, however, indicate an increase in strength. This is due to the ] 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 ]s; 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. ] impregnated with crude resin and dried is also greatly increased in strength thereby.


] produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry ] block 5&nbsp;cm in section, which will sustain a permanent load four times as great as a green (undried) block of the same size will.
] is distinctively red in colour]]
Since the late wood of a growth ring is usually darker in colour than the early wood, 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 late wood, though on cross sections of heartwood the reverse is commonly true. Except in the manner just stated the colour of wood is no indication of strength.


The greatest strength increase due to drying is in the ultimate crushing strength, and strength at ] in endwise compression; these are followed by the modulus of rupture, and stress at elastic limit in cross-bending, while the ] is least affected.<ref name="Record-1914"/>
Abnormal discolouration of wood often denotes a diseased condition, indicating unsoundness. The black check in western ] 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 discolouration is merely an indication of an injury, and in all probability does not of itself affect the properties of the wood. Certain ] impart to wood characteristic colours which thus become symptomatic of weakness; however an attractive effect known as ] produced by this process is often considered a desirable characteristic. Ordinary sap-staining is due to fungous growth, but does not necessarily produce a weakening effect.


===Structure=== ===Structure===
], showing the vessels, rays (white lines) and annual rings: this is intermediate between diffuse-porous and ring-porous, with vessel size declining gradually]]
Wood is a ], ], ] and ] material. It is composed of fibres of ] (40% – 50%) and ] (15% – 25%) impregnated with ] (15% – 30%).<ref> </ref>]
Wood is a ], ], ] and ] (or more specifically, ]) material. It consists of cells, and the cell walls are composed of micro-fibrils of ] (40–50%) and ] (15–25%) impregnated with ] (15–30%).<ref>{{cite web|url=http://treetesting.com/wood_properties_growth_and_structure.htm|title=Wood Properties Growth and Structure 2015|work=treetesting.com|url-status=live|archive-url=https://web.archive.org/web/20160313044617/http://treetesting.com/wood_properties_growth_and_structure.htm|archive-date=March 13, 2016|df=mdy-all}}</ref>
], ]]]


In coniferous or softwood species the wood cells are mostly of one kind, ]s, and as a result the material is much more uniform in structure than that of most hardwoods. There are no ]s ("pores") in coniferous wood such as one sees so prominently in oak and ash, for example. In coniferous or ] species the wood cells are mostly of one kind, ]s, and as a result the material is much more uniform in structure than that of most ]s. 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.<ref>{{cite web|url=https://nationalvetcontent.edu.au/alfresco/d/d/workspace/SpacesStore/b2f0fcee-47cb-4650-b248-f533d73d5428/13_05/toolbox13_05/unit9_selecting_timber/section2_characteristics/lesson2_hardwood.htm|title=Timber Plus Toolbox, Selecting timber, Characteristics of timber, Structure of hardwoods|work=nationalvetcontent.edu.au|url-status=dead|archive-url=https://web.archive.org/web/20140810184152/https://nationalvetcontent.edu.au/alfresco/d/d/workspace/SpacesStore/b2f0fcee-47cb-4650-b248-f533d73d5428/13_05/toolbox13_05/unit9_selecting_timber/section2_characteristics/lesson2_hardwood.htm|archive-date=August 10, 2014|df=mdy-all}}</ref> The water conducting capability is mostly taken care of by ]: in some cases (oak, chestnut, ash) these are quite large and distinct, in others (], ], ]) 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''.<ref name="Sperry-1994">{{cite journal |last=Sperry |first=John S. |author2=Nichols, Kirk L. |author3=Sullivan, June E. |author4=Eastlack, Sondra E. |title=Xylem Embolism in ring-porous, diffuse-porous, and coniferous trees of Northern Utah and Interior Alaska |journal=Ecology |date=1994 |volume=75 |issue=6 |pages=1736–1752 |jstor=1939633 |doi=10.2307/1939633 |bibcode=1994Ecol...75.1736S |url=http://bioweb.biology.utah.edu/sperry/publications/Sperry%20et%20al.%201994%20Ecology.pdf |access-date=November 30, 2018 |archive-date=August 10, 2017 |archive-url=https://web.archive.org/web/20170810100919/http://bioweb.biology.utah.edu/sperry/publications/Sperry%20et%20al.%201994%20Ecology.pdf |url-status=dead }}</ref>
]), showing the vessels, rays (white lines) and annual rings]]
The structure of the hardwoods is more complex.<ref> www.uwsp.edu</ref> They are more or less filled with vessels: in some cases (oak, chestnut, ash) quite large and distinct, in others (], ], ]) too small to be seen plainly without a small 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, ], chestnut, ], hickory, mulberry, and oak, the larger vessels or pores (as cross sections of vessels are called) are localized 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 fibres. These fibres are the elements which give strength and toughness to wood, while the vessels are a source of weakness.


In ring-porous species, such as ash, black locust, ], chestnut, ], hickory, ], and oak,<ref name="Sperry-1994"/> the larger vessels or pores (as cross sections of vessels are called) are localized 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 fibers are the elements which give strength and toughness to wood, while the vessels are a source of weakness.<ref>{{cite book |last1=Record |first1=Samuel James |title=The Mechanical Properties of Wood, Including a Discussion of the Factors Affecting the Mechanical Properties, and Methods of Timber Testing |date=1914 |publisher=J. Wiley & sons, Incorporated |url=https://books.google.com/books?id=IbjPAAAAMAAJ&pg=PA44 |language=en |access-date=March 20, 2023 |archive-date=September 8, 2023 |archive-url=https://web.archive.org/web/20230908234053/https://books.google.com/books?id=IbjPAAAAMAAJ&pg=PA44 |url-status=live }}</ref>
In diffuse-porous woods the pores are scattered throughout the growth ring instead of being collected in a band or row. Examples of this kind of wood are ], ], buckeye, maple, poplar, and willow. Some species, such as ] and ], are on the border between the two classes, forming an intermediate group.


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 ],<ref name="Sperry-1994"/> ],<ref name="SJRecord-1914">{{cite book|author=Samuel James Record|title=The mechanical properties of wood, including a discussion of the factors affecting the mechanical properties, and methods of timber testing|url=https://archive.org/details/mechanicalprope01recogoog|year=1914|publisher=J. Wiley & sons, inc.|pages=–|df=mdy-all}}</ref> ],<ref name="Sperry-1994"/> buckeye, maple, ], and the '']'' species such as aspen, cottonwood and poplar.<ref name="Sperry-1994"/> Some species, such as ] and ], are on the border between the two classes, forming an intermediate group.<ref name="SJRecord-1914"/>
] end grain, showing the '''ring-porous''' structure.]]


===Earlywood and latewood===
If a heavy piece of pine is compared with a light specimen it will be seen at once that the heavier one contains a larger proportion of late wood than the other, and is therefore considerably darker. The late wood of all species is denser than that formed early in the season, hence the greater the proportion of late wood the greater the density and strength. When examined under a microscope the cells of the late wood are seen to be very thick-walled and with very small cavities, while those formed first in the season have thin walls and large cavities. The strength is in the walls, not the cavities. In choosing a piece of pine where strength or stiffness is the important consideration, the principal thing to observe is the comparative amounts of early and late wood. The width of ring is not nearly so important as the proportion of the late wood in the ring.


====In softwood====
It is not only the proportion of late wood, but also its quality, that counts. In specimens that show a very large proportion of late wood it may be noticeably more porous and weigh considerably less than the late wood in pieces that contain but little. One can judge comparative density, and therefore to some extent weight and strength, by visual inspection.
]]]
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 ] 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 ], on the other hand, the latewood is very dense and is deep-colored, presenting a very decided contrast to the soft, straw-colored earlywood.
] tree]]
No satisfactory explanation can as yet be given for the real causes underlying the formation of early and late wood. 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. But in choosing a particular specimen it is not the width of ring, but the proportion and character of the late wood which should govern.


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 less latewood. One can judge comparative density, and therefore to some extent strength, by visual inspection.
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.


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, where strength or ease of working is essential, woods of moderate to slow growth should be chosen.
In ring-porous woods of good growth it is usually the middle portion of the ring in which the thick-walled, strength-giving fibres are most abundant. As the breadth of ring diminishes, this middle portion 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 early wood occupy from 6 to 10 per cent of the volume of the log, while in inferior material they may make up 25 per cent or more. The late wood of good oak, except for ] greyish patches of small pores, is dark coloured and firm, and consists of thick-walled fibres which form one-half or more of the wood. In inferior oak, such fibre areas are much reduced both in quantity and quality. Such variation is very largely the result of rate of growth.


====In ring-porous woods====
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 the ], 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 ]s. 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:
]''; tangential view, wide growth rings]]
:"The work or shock-resisting ability is greatest in wide-ringed wood that has from 5 to 14 rings per ] (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."<ref name=USforest>U.S. Department of Agriculture, Forest Products Laboratory. ''''. General Technical Report 113. Madison, WI.</ref>
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 six to ten 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 ]s. Here not only strength, but toughness and resilience are important.<ref name="Record-1914"/>

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."<ref name="USDA_FPL-2007">U.S. Department of Agriculture, Forest Products Laboratory. '' {{webarchive|url=https://web.archive.org/web/20070315214043/http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm |date=March 15, 2007 }}''. General Technical Report 113. Madison, WI.</ref>


The effect of rate of growth on the qualities of chestnut wood is summarized by the same authority as follows: The effect of rate of growth on the qualities of chestnut wood is summarized 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."<ref name=USforest/> :"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."<ref name="USDA_FPL-2007"/>


====In diffuse-porous woods====
In diffuse-porous woods, as has been stated, the vessels or pores are scattered throughout the ring instead of collected in the early wood. 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, 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 late wood of one season's growth and the early wood of the next.
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===
Structural tissue resembling ordinary 'dicot' wood is produced by a number of ] plants, and these are also usually called wood. Of these, the wood of the grass ] has considerable economic importance, larger culms being used in the manufacture of engineered flooring, panels and ]. Other plant groups that produce woody tissue are ]s, and members of the ], such as ] and ]. With all these woods, the structure and composition of the structural tissue is quite different from ordinary wood.


==Water content== ===Monocots===
] palm, a monocot, in ]. From this perspective these look not much different from trunks of a ] or ]]]
], ] are among a handful of ]s built entirely of wood, without metal joints.]]
Structural material that resembles ordinary, "dicot" or conifer timber in its gross handling characteristics is produced by a number of ] plants, and these also are colloquially called wood. Of these, ], botanically a member of the grass family, has considerable economic importance, larger culms being widely used as a building and construction material and in the manufacture of engineered flooring, panels and ]. Another major plant group that produces material that often is called wood are the ]. Of much less importance are plants such as ''],'' '']'' and ''].'' With all this material, the structure and composition of the processed raw material is quite different from ordinary wood.
] occurs in living wood in the following three conditions: (1) in the ]s, (2) in the ]ic contents of the ], 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 water in the cell walls, and practically none in other forms. Even oven-dried wood retains a small percentage of moisture, but aside from chemical purposes, may be considered absolutely dry.


===Specific gravity===
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 of ]. Within certain limits, the greater the water content, the greater its softening effect.
The single most revealing property of wood as an indicator of wood quality is ] (Timell 1986),<ref name="Timell-1986">Timell, T.E. 1986. Compression wood in gymnosperms. Springer-Verlag, Berlin. 2150 p.</ref> as both pulp yield and lumber strength are determined by it. Specific gravity is the ratio of the mass of a substance to the mass of an equal volume of water; density is the ratio of a mass of a quantity of a substance to the volume of that quantity and is expressed in mass per unit substance, e.g., grams per milliliter (g/cm<sup>3</sup> or g/ml). The terms are essentially equivalent as long as the metric system is used. Upon drying, wood shrinks and its density increases. Minimum values are associated with green (water-saturated) wood and are referred to as ''basic specific gravity'' (Timell 1986).<ref name="Timell-1986" />


The U.S. ] lists a variety of ways to define specific gravity (G) and density (ρ) for wood:<ref>{{Cite web |title=Wood Handbook: Chapter 4: Moisture Relations and Physical Properties of Wood |url=https://www.fpl.fs.usda.gov/documnts/fplgtr/fplgtr282/chapter_04_fpl_gtr282.pdf |publisher=U.S. Forest Products Laboratory |access-date=September 10, 2023 |archive-date=December 30, 2023 |archive-url=https://web.archive.org/web/20231230131945/https://www.fpl.fs.usda.gov/documnts/fplgtr/fplgtr282/chapter_04_fpl_gtr282.pdf |url-status=live }}</ref>
Drying produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry ] block 5 cm in section, which will sustain a permanent load four times as great as that which a green block of the same size will support.
{| class="wikitable"
!Symbol
!Mass basis
!Volume basis
|-
|G<sub>0</sub>
|Ovendry
|Ovendry
|-
|G<sub>b</sub> (basic)
|Ovendry
|Green
|-
|G<sub>12</sub>
|Ovendry
|12% MC
|-
|G<sub>x</sub>
|Ovendry
|x% MC
|-
|ρ<sub>0</sub>
|Ovendry
|Ovendry
|-
|ρ<sub>12</sub>
|12% MC
|12% MC
|-
|ρ<sub>x</sub>
|x% MC
|x% MC
|}
The FPL has adopted G<sub>b</sub> and G<sub>12</sub> for specific gravity, in accordance with the ] D2555<ref>{{Cite web |title=Standard Practice for Establishing Clear Wood Strength Values |url=https://www.astm.org/d2555-17a.html |access-date=2023-09-09 |website=www.astm.org |language=en |archive-date=April 1, 2023 |archive-url=https://web.archive.org/web/20230401232343/https://www.astm.org/d2555-17a.html |url-status=live }}</ref> standard. These are scientifically useful, but don't represent any condition that could physically occur. The FPL Wood Handbook also provides formulas for approximately converting any of these measurements to any other.


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

{{See also|Janka hardness test}}

Wood density is determined by multiple growth and physiological factors compounded into "one fairly easily measured wood characteristic" (Elliott 1970).<ref name="Elliott-1970">Elliott, G.K. 1970. Wood density in conifers. Commonwealth For. Bureau, Oxford, U.K., Tech. Commun. 8. 44 p.</ref>

Age, diameter, height, radial (trunk) growth, geographical location, site and growing conditions, ] treatment, and seed source all to some degree influence wood density. Variation is to be expected. Within an individual tree, the variation in wood density is often as great as or even greater than that between different trees (Timell 1986).<ref name="Timell-1986" /> Variation of specific gravity within the ] of a tree can occur in either the horizontal or vertical direction.

Because the specific gravity as defined above uses an unrealistic condition, woodworkers tend to use the "average dried weight", which is a density based on mass at 12% moisture content and volume at the same (ρ<sub>12</sub>). This condition occurs when the wood is at equilibrium moisture content with air at about 65% relative humidity and temperature at 30&nbsp;°C (86&nbsp;°F). This density is expressed in units of kg/m<sup>3</sup> or lbs/ft<sup>3</sup>.

===Tables===
The following tables list the mechanical properties of wood and lumber plant species, including bamboo. See also ] for additional properties.

Wood properties:<ref>{{Cite tech report |first=D.W. |last=Green |first2=J.E. |last2=Winandy |first3=D.E. |last3=Kretschmann |chapter=4. Mechanical Properties of Wood |chapter-url=https://www.fpl.fs.usda.gov/documnts/fplgtr/fplgtr113/ch04.pdf |title=Wood handbook: Wood as an engineering material |publisher=U.S. Department of Agriculture, Forest Service, Forest Products Laboratory |year=1999 |id=FPL–GTR–113 |pages=463 |url=https://www.fs.usda.gov/research/treesearch/5734 |doi=10.2737/FPL-GTR-113|hdl=2027/mdp.39015000158041 |hdl-access=free }}</ref><ref name="pfaf-2019" />
{|class="wikitable mw-collapsible mw-collapsed sortable"
!'''Common name'''
!'''Scientific name'''
!'''Moisture content'''
!'''Density (kg/m<sup>3</sup>)'''
!'''Compressive strength (megapascals)'''
!'''Flexural strength (megapascals)'''
|-
|Red Alder
|'']''
|Green
|370
|20.4
|45
|-
|Red Alder
|'']''
|12.00%
|410
|40.1
|68
|-
|Black Ash
|'']''
|Green
|450
|15.9
|41
|-
|Black Ash
|'']''
|12.00%
|490
|41.2
|87
|-
|Blue Ash
|'']''
|Green
|530
|24.8
|66
|-
|Blue Ash
|'']''
|12.00%
|580
|48.1
|95
|-
|Green Ash
|'']''
|Green
|530
|29
|66
|-
|Green Ash
|'']''
|12.00%
|560
|48.8
|97
|-
|Oregon Ash
|'']''
|Green
|500
|24.2
|52
|-
|Oregon Ash
|'']''
|12.00%
|550
|41.6
|88
|-
|White Ash
|'']''
|Green
|550
|27.5
|66
|-
|White Ash
|'']''
|12.00%
|600
|51.1
|103
|-
|Bigtooth Aspen
|'']''
|Green
|360
|17.2
|37
|-
|Bigtooth Aspen
|'']''
|12.00%
|390
|36.5
|63
|-
|Quaking Aspen
|'']''
|Green
|350
|14.8
|35
|-
|Quaking Aspen
|'']''
|12.00%
|380
|29.3
|58
|-
|American Basswood
|'']''
|Green
|320
|15.3
|34
|-
|American Basswood
|'']''
|12.00%
|370
|32.6
|60
|-
|American Beech
|'']''
|Green
|560
|24.5
|59
|-
|American Beech
|'']''
|12.00%
|640
|50.3
|103
|-
|Paper Birch
|'']''
|Green
|480
|16.3
|44
|-
|Paper Birch
|'']''
|12.00%
|550
|39.2
|85
|-
|Sweet Birch
|'']''
|Green
|600
|25.8
|65
|-
|Sweet Birch
|'']''
|12.00%
|650
|58.9
|117
|-
|Yellow Birch
|'']''
|Green
|550
|23.3
|57
|-
|Yellow Birch
|'']''
|12.00%
|620
|56.3
|114
|-
|Butternut
|'']''
|Green
|360
|16.7
|37
|-
|Butternut
|'']''
|12.00%
|380
|36.2
|56
|-
|Black Cherry
|'']''
|Green
|470
|24.4
|55
|-
|Blach Cherry
|'']''
|12.00%
|500
|49
|85
|-
|American Chestnut
|'']''
|Green
|400
|17
|39
|-
|American Chestnut
|'']''
|12.00%
|430
|36.7
|59
|-
|Balsam Poplar Cottonwood
|'']''
|Green
|310
|11.7
|27
|-
|Balsam Poplar Cottonwood
|'']''
|12.00%
|340
|27.7
|47
|-
|Black Cottonwood
|'']''
|Green
|310
|15.2
|34
|-
|Black Cottonwood
|'']''
|12.00%
|350
|31
|59
|-
|Eastern Cottonwood
|'']''
|Green
|370
|15.7
|37
|-
|Eastern Cottonwood
|'']''
|12.00%
|400
|33.9
|59
|-
|American Elm
|'']''
|Green
|460
|20.1
|50
|-
|American Elm
|'']''
|12.00%
|500
|38.1
|81
|-
|Rock Elm
|'']''
|Green
|570
|26.1
|66
|-
|Rock Elm
|'']''
|12.00%
|630
|48.6
|102
|-
|Slippery Elm
|'']''
|Green
|480
|22.9
|55
|-
|Slippery Elm
|'']''
|12.00%
|530
|43.9
|90
|-
|Hackberry
|'']''
|Green
|490
|18.3
|45
|-
|Hackberry
|'']''
|12.00%
|530
|37.5
|76
|-
|Bitternut Hickory
|'']''
|Green
|600
|31.5
|71
|-
|Bitternut Hickory
|'']''
|12.00%
|660
|62.3
|118
|-
|Nutmeg Hickory
|'']''
|Green
|560
|27.4
|63
|-
|Nutmeg Hickory
|'']''
|12.00%
|600
|47.6
|114
|-
|Pecan Hickory
|'']''
|Green
|600
|27.5
|68
|-
|Pecan Hickory
|'']''
|12.00%
|660
|54.1
|94
|-
|Water Hickory
|'']''
|Green
|610
|32.1
|74
|-
|Water Hickory
|'']''
|12.00%
|620
|59.3
|123
|-
|Mockernut Hickory
|'']''
|Green
|640
|30.9
|77
|-
|Mockernut Hickory
|'']''
|12.00%
|720
|61.6
|132
|-
|Pignut Hickory
|'']''
|Green
|660
|33.2
|81
|-
|Pignut Hickory
|'']''
|12.00%
|750
|63.4
|139
|-
|Shagbark Hickory
|'']''
|Green
|640
|31.6
|76
|-
|Shagbark Hickory
|'']''
|12.00%
|720
|63.5
|139
|-
|Shellbark Hickory
|'']''
|Green
|620
|27
|72
|-
|Shellbark Hickory
|'']''
|12.00%
|690
|55.2
|125
|-
|Honeylocust
|'']''
|Green
|600
|30.5
|70
|-
|Honeylocust
|'']''
|12.00%
|600
|51.7
|101
|-
|Black Locust
|'']''
|Green
|660
|46.9
|95
|-
|Black Locust
|'']''
|12.00%
|690
|70.2
|134
|-
|Cucumber Tree Magnolia
|'']''
|Green
|440
|21.6
|51
|-
|Cucumber Tree Magnolia
|'']''
|12.00%
|480
|43.5
|85
|-
|Southern Magnolia
|'']''
|Green
|460
|18.6
|47
|-
|Southern Magnolia
|'']''
|12.00%
|500
|37.6
|77
|-
|Bigleaf Maple
|'']''
|Green
|440
|22.3
|51
|-
|Bigleaf Maple
|'']''
|12.00%
|480
|41
|74
|-
|Black Maple
|'']''
|Green
|520
|22.5
|54
|-
|Black Maple
|'']''
|12.00%
|570
|46.1
|92
|-
|Red Maple
|'']''
|Green
|490
|22.6
|53
|-
|Red Maple
|'']''
|12.00%
|540
|45.1
|92
|-
|Silver Maple
|'']''
|Green
|440
|17.2
|40
|-
|Silver Maple
|'']''
|12.00%
|470
|36
|61
|-
|Sugar Maple
|'']''
|Green
|560
|27.7
|65
|-
|Sugar Maple
|'']''
|12.00%
|630
|54
|109
|-
|Black Red Oak
|'']''
|Green
|560
|23.9
|57
|-
|Black Red Oak
|'']''
|12.00%
|610
|45
|96
|-
|Cherrybark Red Oak
|'']''
|Green
|610
|31.9
|74
|-
|Cherrybark Red Oak
|'']''
|12.00%
|680
|60.3
|125
|-
|Laurel Red Oak
|'']''
|Green
|560
|21.9
|54
|-
|Laurel Red Oak
|'']''
|12.00%
|630
|48.1
|87
|-
|Northern Red Oak
|'']''
|Green
|560
|23.7
|57
|-
|Northern Red Oak
|'']''
|12.00%
|630
|46.6
|99
|-
|Pin Red Oak
|'']''
|Green
|580
|25.4
|57
|-
|Pin Red Oak
|'']''
|12.00%
|630
|47
|97
|-
|Scarlet Red Oak
|'']''
|Green
|600
|28.2
|72
|-
|Scarlet Red Oak
|'']''
|12.00%
|670
|57.4
|120
|-
|Southern Red Oak
|'']''
|Green
|520
|20.9
|48
|-
|Southern Red Oak
|'']''
|12.00%
|590
|42
|75
|-
|Water Red Oak
|'']''
|Green
|560
|25.8
|61
|-
|Water Red Oak
|'']''
|12.00%
|630
|46.7
|106
|-
|Willow Red Oak
|'']''
|Green
|560
|20.7
|51
|-
|Willow Red Oak
|'']''
|12.00%
|690
|48.5
|100
|-
|Bur White Oak
|'']''
|Green
|580
|22.7
|50
|-
|Bur White Oak
|'']''
|12.00%
|640
|41.8
|71
|-
|Chestnut White Oak
|'']''
|Green
|570
|24.3
|55
|-
|Chestnut White Oak
|'']''
|12.00%
|660
|47.1
|92
|-
|Live White Oak
|'']''
|Green
|800
|37.4
|82
|-
|Live White Oak
|'']''
|12.00%
|880
|61.4
|127
|-
|Overcup White Oak
|'']''
|Green
|570
|23.2
|55
|-
|Overcup White Oak
|'']''
|12.00%
|630
|42.7
|87
|-
|Post White Oak
|'']''
|Green
|600
|24
|56
|-
|Post White Oak
|'']''
|12.00%
|670
|45.3
|91
|-
|Swamp Chestnut White Oak
|'']''
|Green
|600
|24.4
|59
|-
|Swamp Chestnut White Oak
|'']''
|12.00%
|670
|50.1
|96
|-
|Swamp White Oak
|'']''
|Green
|640
|30.1
|68
|-
|Swamp White Oak
|'']''
|12.00%
|720
|59.3
|122
|-
|White Oak
|'']''
|Green
|600
|24.5
|57
|-
|White Oak
|'']''
|12.00%
|680
|51.3
|105
|-
|Sassafras
|'']''
|Green
|420
|18.8
|41
|-
|Sassafras
|'']''
|12.00%
|460
|32.8
|62
|-
|Sweetgum
|'']''
|Green
|460
|21
|49
|-
|Sweetgum
|'']''
|12.00%
|520
|43.6
|86
|-
|American Sycamore
|'']''
|Green
|460
|20.1
|45
|-
|American Sycamore
|'']''
|12.00%
|490
|37.1
|69
|-
|Tanoak
|'']''
|Green
|580
|32.1
|72
|-
|Tanoak
|'']''
|12.00%
|580
|32.1
|72
|-
|Black Tupelo
|'']''
|Green
|460
|21
|48
|-
|Black Tupelo
|'']''
|12.00%
|500
|38.1
|66
|-
|Water Tupelo
|'']''
|Green
|460
|23.2
|50
|-
|Water Tupelo
|'']''
|12.00%
|500
|40.8
|66
|-
|Black Walnut
|'']''
|Green
|510
|29.6
|66
|-
|Black Walnut
|'']''
|12.00%
|550
|52.3
|101
|-
|Black Willow
|'']''
|Green
|360
|14.1
|33
|-
|Black Willow
|'']''
|12.00%
|390
|28.3
|54
|-
|Yellow Poplar
|'']''
|Green
|400
|18.3
|41
|-
|Yellow Poplar
|'']''
|12.00%
|420
|38.2
|70
|-
|Baldcypress
|'']''
|Green
|420
|24.7
|46
|-
|Baldcypress
|'']''
|12.00%
|460
|43.9
|73
|-
|Atlantic White Cedar
|'']''
|Green
|310
|16.5
|32
|-
|Atlantic White Cedar
|'']''
|12.00%
|320
|32.4
|47
|-
|Eastern Redcedar
|'']''
|Green
|440
|24.6
|48
|-
|Eastern Redcedar
|'']''
|12.00%
|470
|41.5
|61
|-
|Incense Cedar
|'']''
|Green
|350
|21.7
|43
|-
|Incense Cedar
|'']''
|12.00%
|370
|35.9
|55
|-
|Northern White Cedar
|'']''
|Green
|290
|13.7
|29
|-
|Northern White Cedar
|'']''
|12.00%
|310
|27.3
|45
|-
|Port Orford Cedar
|'']''
|Green
|390
|21.6
|45
|-
|Port Orford Cedar
|'']''
|12.00%
|430
|43.1
|88
|-
|Western Redcedar
|'']''
|Green
|310
|19.1
|35.9
|-
|Western Redcedar
|'']''
|12.00%
|320
|31.4
|51.7
|-
|Yellow Cedar
|'']''
|Green
|420
|21
|44
|-
|Yellow Cedar
|'']''
|12.00%
|440
|43.5
|77
|-
|Coast Douglas Fir
|'']''
|Green
|450
|26.1
|53
|-
|Coast Douglas Fir
|'']''
|12.00%
|480
|49.9
|85
|-
|Interior West Douglas Fir
|'']''
|Green
|460
|26.7
|53
|-
|Interior West Douglas Fir
|'']''
|12.00%
|500
|51.2
|87
|-
|Interior North Douglas Fir
|'']''
|Green
|450
|23.9
|51
|-
|Interior North Douglas Fir
|'']''
|12.00%
|480
|47.6
|90
|-
|Interior South Douglas Fir
|'']''
|Green
|430
|21.4
|47
|-
|Interior South Douglas Fir
|'']''
|12.00%
|460
|43
|82
|-
|Balsam Fir
|'']''
|Green
|330
|18.1
|38
|-
|Balsam Fir
|'']''
|12.00%
|350
|36.4
|63
|-
|California Red Fir
|'']''
|Green
|360
|19
|40
|-
|California Red Fir
|'']''
|12.00%
|380
|37.6
|72.4
|-
|Grand Fir
|'']''
|Green
|350
|20.3
|40
|-
|Grand Fir
|'']''
|12.00%
|370
|36.5
|61.4
|-
|Noble Fir
|'']''
|Green
|370
|20.8
|43
|-
|Noble Fir
|'']''
|12.00%
|390
|42.1
|74
|-
|Pacific Silver Fir
|'']''
|Green
|400
|21.6
|44
|-
|Pacific Silver Fir
|'']''
|12.00%
|430
|44.2
|75
|-
|Subalpine Fir
|'']''
|Green
|310
|15.9
|34
|-
|Subalpine Fir
|'']''
|12.00%
|320
|33.5
|59
|-
|White Fir
|'']''
|Green
|370
|20
|41
|-
|White Fir
|'']''
|12.00%
|390
|40
|68
|-
|Eastern Hemlock
|'']''
|Green
|380
|21.2
|44
|-
|Eastern Hemlock
|'']''
|12.00%
|400
|37.3
|61
|-
|Mountain Hemlock
|'']''
|Green
|420
|19.9
|43
|-
|Mountain Hemlock
|'']''
|12.00%
|450
|44.4
|79
|-
|Western Hemlock
|'']''
|Green
|420
|23.2
|46
|-
|Western Hemlock
|'']''
|12.00%
|450
|49
|78
|-
|Western Larch
|'']''
|Green
|480
|25.9
|53
|-
|Western Larch
|'']''
|12.00%
|520
|52.5
|90
|-
|Eastern White Pine
|'']''
|Green
|340
|16.8
|34
|-
|Eastern White Pine
|'']''
|12.00%
|350
|33.1
|59
|-
|Jack Pine
|'']''
|Green
|400
|20.3
|41
|-
|Jack Pine
|'']''
|12.00%
|430
|39
|68
|-
|Loblolly Pine
|'']''
|Green
|470
|24.2
|50
|-
|Loblolly Pine
|'']''
|12.00%
|510
|49.2
|88
|-
|Lodgepole Pine
|'']''
|Green
|380
|18
|38
|-
|Lodgepole Pine
|'']''
|12.00%
|410
|37
|65
|-
|Longleaf Pine
|'']''
|Green
|540
|29.8
|59
|-
|Longleaf Pine
|'']''
|12.00%
|590
|58.4
|100
|-
|Pitch Pine
|'']''
|Green
|470
|20.3
|47
|-
|Pitch Pine
|'']''
|12.00%
|520
|41
|74
|-
|Pond Pine
|'']''
|Green
|510
|25.2
|51
|-
|Pond Pine
|'']''
|12.00%
|560
|52
|80
|-
|Ponderosa Pine
|'']''
|Green
|380
|16.9
|35
|-
|Ponderosa Pine
|'']''
|12.00%
|400
|36.7
|65
|-
|Red Pine
|'']''
|Green
|410
|18.8
|40
|-
|Red Pine
|'']''
|12.00%
|460
|41.9
|76
|-
|Sand Pine
|'']''
|Green
|460
|23.7
|52
|-
|Sand Pine
|'']''
|12.00%
|480
|47.7
|80
|-
|Shortleaf Pine
|'']''
|Green
|470
|24.3
|51
|-
|Shortleaf Pine
|'']''
|12.00%
|510
|50.1
|90
|-
|Slash Pine
|'']''
|Green
|540
|26.3
|60
|-
|Slash Pine
|'']''
|12.00%
|590
|56.1
|112
|-
|Spruce Pine
|'']''
|Green
|410
|19.6
|41
|-
|Spruce Pine
|'']''
|12.00%
|440
|39
|72
|-
|Sugar Pine
|'']''
|Green
|340
|17
|34
|-
|Sugar Pine
|'']''
|12.00%
|360
|30.8
|57
|-
|Virginia Pine
|'']''
|Green
|450
|23.6
|50
|-
|Virginia Pine
|'']''
|12.00%
|480
|46.3
|90
|-
|Western White Pine
|'']''
|Green
|360
|16.8
|32
|-
|Western White Pine
|'']''
|12.00%
|380
|34.7
|67
|-
|Redwood Old Growth
|'']''
|Green
|380
|29
|52
|-
|Redwood Old Growth
|'']''
|12.00%
|400
|42.4
|69
|-
|Redwood New Growth
|'']''
|Green
|340
|21.4
|41
|-
|Redwood New Growth
|'']''
|12.00%
|350
|36
|54
|-
|Black Spruce
|'']''
|Green
|380
|19.6
|42
|-
|Black Spruce
|'']''
|12.00%
|460
|41.1
|74
|-
|Engelmann Spruce
|'']''
|Green
|330
|15
|32
|-
|Engelmann Spruce
|'']''
|12.00%
|350
|30.9
|64
|-
|Red Spruce
|'']''
|Green
|370
|18.8
|41
|-
|Red Spruce
|'']''
|12.00%
|400
|38.2
|74
|-
|Sitka Spruce
|'']''
|Green
|330
|16.2
|34
|-
|Sitka Spruce
|'']''
|12.00%
|360
|35.7
|65
|-
|White Spruce
|'']''
|Green
|370
|17.7
|39
|-
|White Spruce
|'']''
|12.00%
|400
|37.7
|68
|-
|Tamarack Spruce
|'']''
|Green
|490
|24
|50
|-
|Tamarack Spruce
|'']''
|12.00%
|530
|49.4
|80
|}
Bamboo properties:<ref>{{Cite web|title=What are the mechanical properties of bamboo|url=https://doorstain.com/blog/news/what-are-the-mechanical-properties-of-bamboo/|access-date=2023-08-22|website=www.DoorStain.com|date=August 22, 2023 |archive-date=August 22, 2023|archive-url=https://web.archive.org/web/20230822211225/https://doorstain.com/blog/news/what-are-the-mechanical-properties-of-bamboo/|url-status=live}}</ref><ref name="pfaf-2019">{{Cite web|url=https://pfaf.org/user/Default.aspx|title=PFAF|website=pfaf.org|access-date=2019-11-03|archive-date=October 24, 2019|archive-url=https://web.archive.org/web/20191024204115/https://pfaf.org/user/default.aspx|url-status=live}}</ref>
{|class="wikitable mw-collapsible mw-collapsed sortable"
!'''Common name'''
!'''Scientific name'''
!'''Moisture content'''
!'''Density (kg/m<sup>3</sup>)'''
!'''Compressive strength (megapascals)'''
!'''Flexural strength (megapascals)'''
|-
|Balku bans
|'']''
|green
|
|45
|73.7
|-
|Balku bans
|'']''
|air dry
|
|54.15
|81.1
|-
|Balku bans
|'']''
|8.5
|820
|69
|151
|-
|Indian thorny bamboo
|'']''
|9.5
|710
|61
|143
|-
|Indian thorny bamboo
|'']''
|
|
|43.05
|37.15
|-
|Nodding Bamboo
|'']''
|8
|890
|75
|52.9
|-
|Nodding Bamboo
|'']''
|87
|
|46
|52.4
|-
|Nodding Bamboo
|'']''
|12
|
|85
|67.5
|-
|Nodding Bamboo
|'']''
|88.3
|
|44.7
|88
|-
|Nodding Bamboo
|'']''
|14
|
|47.9
|216
|-
|Clumping Bamboo
|'']''
|
|
|45.8
|
|-
|Clumping Bamboo
|'']''
|5
|
|79
|80
|-
|Clumping Bamboo
|'']''
|20
|
|35
|37
|-
|Burmese bamboo
|'']''
|95.1
|
|32.1
|28.3
|-
|
|'']''
|air dry
|
|57
|51.77
|-
|Indian timber bamboo
|'']''
|73.6
|
|40.7
|51.1
|-
|Indian timber bamboo
|'']''
|11.9
|
|68
|66.7
|-
|Indian timber bamboo
|'']''
|8.6
|910
|79
|194
|-
|dragon bamboo
|'']''
|8
|740
|70
|193
|-
|Hamilton's bamboo
|'']''
|8.5
|590
|70
|89
|-
|White bamboo
|'']''
|102
|
|40.5
|26.3
|-
|String Bamboo
|'']''
|54.3
|
|24.1
|102
|-
|String Bamboo
|'']''
|15.1
|
|37.95
|87.5
|-
|Java Black Bamboo
|'']''
|54
|
|23.8
|92.3
|-
|Java Black Bamboo
|'']''
|15
|
|35.7
|94.1
|-
|Giant Atter
|'']''
|72.3
|
|26.4
|98
|-
|Giant Atter
|'']''
|14.4
|
|31.95
|122.7
|-
|
|'']''
|8
|960
|71
|154
|-
|American Narrow-Leaved Bamboo
|'']''
|
|
|42
|53.5
|-
|American Narrow-Leaved Bamboo
|'']''
|
|
|63.6
|144.8
|-
|American Narrow-Leaved Bamboo
|'']''
|
|
|86.3
|46
|-
|American Narrow-Leaved Bamboo
|'']''
|
|
|77.5
|82
|-
|American Narrow-Leaved Bamboo
|'']''
|15
|
|56
|87
|-
|American Narrow-Leaved Bamboo
|'']''
|
|
|63.3
|
|-
|American Narrow-Leaved Bamboo
|'']''
|
|
|28
|
|-
|American Narrow-Leaved Bamboo
|'']''
|
|
|56.2
|
|-
|American Narrow-Leaved Bamboo
|'']''
|
|
|38
|
|-
|Berry Bamboo
|'']''
|12.8
|
|69.9
|57.6
|-
|Japanese timber bamboo
|'']''
|
|
|51
|
|-
|Japanese timber bamboo
|'']''
|8
|730
|63
|
|-
|Japanese timber bamboo
|'']''
|64
|
|44
|
|-
|Japanese timber bamboo
|'']''
|61
|
|40
|
|-
|Japanese timber bamboo
|'']''
|9
|
|71
|
|-
|Japanese timber bamboo
|'']''
|9
|
|74
|
|-
|Japanese timber bamboo
|'']''
|12
|
|54
|
|-
|Tortoise shell bamboo
|'']''
|
|
|44.6
|
|-
|Tortoise shell bamboo
|'']''
|75
|
|67
|
|-
|Tortoise shell bamboo
|'']''
|15
|
|71
|
|-
|Tortoise shell bamboo
|'']''
|6
|
|108
|
|-
|Tortoise shell bamboo
|'']''
|0.2
|
|147
|
|-
|Tortoise shell bamboo
|'']''
|5
|
|117
|51
|-
|Tortoise shell bamboo
|'']''
|30
|
|44
|55
|-
|Tortoise shell bamboo
|'']''
|12.5
|603
|60.3
|
|-
|Tortoise shell bamboo
|'']''
|10.3
|530
|
|83
|-
|Early Bamboo
|'']''
|28.5
|827
|79.3
|
|-
|Oliveri
|'']''
|53
|
|46.9
|61.9
|-
|Oliveri
|'']''
|7.8
|
|58
|90
|}

==Hard versus soft==

It is common to classify wood as either ] or ]. The wood from ] (e.g. pine) is called softwood, and the wood from ] (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. ]) are harder than many hardwoods.

There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it, at least for certain species. For example, in loblolly pine, wind exposure and stem position greatly affect the hardness of wood, as well as compression wood content.<ref>{{cite book |title=Agriculture Handbook |date=1997 |publisher=U.S. Department of Agriculture |pages=2–6 |url=https://books.google.com/books?id=MeAstagRCJ4C&pg=SA2-PA6 |language=en |access-date=March 20, 2023 |archive-date=September 8, 2023 |archive-url=https://web.archive.org/web/20230908234052/https://books.google.com/books?id=MeAstagRCJ4C&pg=SA2-PA6 |url-status=live }}</ref> The density of wood varies with species. The density of a wood correlates with its strength (mechanical properties). For example, ] is a medium-dense hardwood that is excellent for fine furniture crafting, whereas ] is light, making it useful for ] building. One of the densest woods is ].

==Chemistry==
], which makes up about 25% of wood dry matter and is responsible for many of its properties.]]
The chemical composition of wood varies from species to species, but is approximately 50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other elements (mainly ], ], ], ], ], and ]) by weight.<ref>{{cite book|title=Mémotech Bois et Matériaux Associés|date=1996|publisher=Éditions Casteilla|location=Paris|isbn=978-2-7135-1645-0|page=22|author= Jean-Pierre Barette|author2= Claude Hazard et Jérôme Mayer}}</ref> Wood also contains ], ], ], ], and other elements in small quantity.

Aside from water, wood has three main components. ], a crystalline polymer derived from glucose, constitutes about 41–43%. Next in abundance is ], which is around 20% in deciduous trees but near 30% in conifers. It is mainly ] that are linked in an irregular manner, in contrast to the cellulose. ] 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 ]s. 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.

In chemical terms, the difference between hardwood and softwood is reflected in the composition of the constituent ]. Hardwood lignin is primarily derived from ] and ]. Softwood lignin is mainly derived from coniferyl alcohol.<ref name="Boerjan-2003">{{cite journal| author = W. Boerjan| author2 = J. Ralph| author3 = M. Baucher|date=June 2003| title = Lignin biosynthesis| journal = Annu. Rev. Plant Biol.| volume = 54| issue = 1| pages = 519–549| doi = 10.1146/annurev.arplant.54.031902.134938| pmid = 14503002}}</ref>

===Extractives===
Aside from the structural ]s, i.e. ], ] and ] (]), wood contains a large variety of non-structural constituents, composed of low ] ]s, called ''extractives''. These compounds are present in the ] and can be extracted from the wood using different neutral ]s, such as ].<ref name="Ek-2009">{{cite book |last1=Ek |first1=Monica |last2=Gellerstedt |first2=Göran |last3=Henriksson |first3=Gunnar |title=Pulp and Paper Chemistry and Technology. Volume 1, Wood Chemistry and Wood Biotechnology |date=2009 |publisher=Walter de Gruyter |location=Berlin |isbn=978-3-11-021339-3 |chapter=Chapter 7: Wood extractives}}</ref> Analogous content is present in the so-called ''exudate'' produced by trees in response to mechanical damage or after being attacked by ]s or ].<ref name="Sjöström-2013">{{cite book |last1=Sjöström |first1=Eero |title=Wood Chemistry: Fundamentals and Applications |publisher=Elsevier Science |location=San Diego |isbn=978-0-08-092589-9 |edition=Second |chapter=Chapter 5: Extractives|date=October 22, 2013 }}</ref> Unlike the structural constituents, the composition of extractives varies over wide ranges and depends on many factors.<ref>{{cite book |last1=Ansell |first1=Martin P. |title=Woodhead Publishing Series in Composites Science and Engineering: Number 54. Wood Composites |date=2015 |publisher=Woodhead Publishing |location=Cambridge, UK |isbn=978-1-78242-454-3 |chapter=Chapter 11: Preservation, Protection and Modification of Wood Composites}}</ref> The amount and composition of extractives differs between tree species, various parts of the same tree, and depends on genetic factors and growth conditions, such as climate and geography.<ref name="Ek-2009" /> For example, slower growing trees and higher parts of trees have higher content of extractives. Generally, the ] is richer in extractives than the ]. Their concentration increases from the ] to the ]. ]s and ]es also contain extractives. Although extractives represent a small fraction of the wood content, usually less than 10%, they are extraordinarily diverse and thus characterize the chemistry of the wood species.<ref name="Hon-2001">{{cite book |last1=Hon |first1=David N.-S. |last2=Shiraishi |first2=Nubuo |title=Wood and Cellulosic Chemistry |date=2001 |publisher=Marcel Dekker |location=New York |isbn=0-8247-0024-4 |edition=2nd, rev. and expanded |chapter=Chapter 6: Chemistry of Extractives}}</ref> Most extractives are secondary metabolites and some of them serve as precursors to other chemicals. Wood extractives display different activities, some of them are produced in response to wounds, and some of them participate in natural defense against insects and fungi.<ref>{{cite book |last1=Rowell |first1=Roger M. |title=Handbook of Wood Chemistry and Wood Composites |date=2013 |publisher=Taylor & Francis |location=Boca Raton |isbn=9781439853801 |edition=2nd |chapter=Chater 3: Cell Wall Chemistry}}</ref>

] refinery in ], Finland]]
These compounds contribute to various physical and chemical properties of the wood, such as wood color, fragnance, durability, acoustic properties, ], adhesion, and drying.<ref name="Hon-2001" /> Considering these impacts, wood extractives also affect the properties of ] and paper, and importantly cause many problems in ]. Some extractives are surface-active substances and unavoidably affect the surface properties of paper, such as water adsorption, friction and strength.<ref name="Ek-2009" /> ] extractives often give rise to sticky deposits during ] and may leave spots on paper. Extractives also account for paper smell, which is important when making ].

Most wood extractives are ] and only a little part is water-soluble.<ref name="Sjöström-2013" /> The lipophilic portion of extractives, which is collectively referred as wood ], contains ]s and ]s, ]s and steryl esters, ]s, ]s, ]s, and ]es.<ref>{{cite book |last = Mimms |first = Agneta |author2=Michael J. Kuckurek |author3=Jef A. Pyiatte |author4=Elizabeth E. Wright |title = Kraft Pulping. A Compilation of Notes |publisher = TAPPI Press |date = 1993 |pages = 6–7 |isbn = 978-0-89852-322-5 }}</ref> The heating of resin, i.e. ], vaporizes the ] terpenes and leaves the solid component – ]. The concentrated liquid of volatile compounds extracted during ] is called ]. Distillation of ] obtained from many ] provides ] and ].<ref>{{cite book |doi=10.1002/14356007.a23_073 |chapter=Resins, Natural |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2000 |last1=Fiebach |first1=Klemens |last2=Grimm |first2=Dieter |isbn=978-3-527-30673-2}}</ref>

Most extractives can be categorized into three groups: ]s, ]s and ].<ref name="Ek-2009" /> The latter are more water-soluble and usually are absent in the resin.
*]s include fatty acids, ]s and their esters with ], fatty alcohols (waxes) and sterols (steryl esters). ]s, such as ]s, are also present in the wood. ] is a polyester, made of suberin acids and glycerol, mainly found in ]s. Fats serve as a source of energy for the wood cells.<ref name="Sjöström-2013" /> The most common wood sterol is ], and less commonly ], citrostadienol, ] or ].<ref name="Ek-2009" />
*The main ]s occurring in the softwood include ], ] and ]s.<ref name="Sjöström-2013" /> Meanwhile, the terpene composition of the hardwood is considerably different, consisting of ]s, ]s and other higher terpenes. Examples of mono-, di- and sesquiterpenes are ] and ]s, ], ], ], ]s, α- and β-]s, α-muurolene, ], ] and ]s, α- and β-]s, juniperol, ], ''cis''-abienol, ], pinifolic acid, nootkatin, chanootin, ], geranyl-linalool, β-epimanool, manoyloxide, pimaral and pimarol. Resin acids are usually ] ]s, examples of which are ], sandaracopimaric acid, ], ], ], palustric acid, neoabietic acid and dehydroabietic acid. ] resin acids are also found, such as lambertianic acid, communic acid, mercusic acid and secodehydroabietic acid. ], ] and ] are ]s purified from hardwood. Examples of wood polyterpenes are ] (''cis''-polypren), ] (''trans''-polypren), gutta-balatá (''trans''-polypren) and betulaprenols (] polyterpenoids).<ref name="Ek-2009" /><ref name="Sjöström-2013" /> The mono- and sesquiterpenes of the softwood are responsible for the typical smell of ] forest.<ref name="Ek-2009" /> Many monoterpenoids, such as ], are used in the preparation of ]s and ].<ref name="Sjöström-2013" /> ]s, such as ] and other ]s, are present in ]-resistant trees and display ] and ] properties. Tropolones strongly bind metal ions and can cause digester ] in the process ]. Owing to their ] and ] properties, especially thujaplicins are used in physiology experiments.<ref>{{cite book |title=Cell physiology sourcebook: essentials of membrane biophysics |location=London, UK |isbn=978-0-12-387738-3 |edition=Fourth |chapter=Chapter 4: Ionophores in Planar Lipid Bilayers |chapter-url=https://www.sciencedirect.com/science/article/pii/B9780123877383000044 |last1=Sperelakis |first1=Nicholas |last2=Sperelakis |first2=Nick |date=January 11, 2012 |access-date=September 27, 2020 |archive-date=June 28, 2020 |archive-url=https://web.archive.org/web/20200628201941/https://www.sciencedirect.com/science/article/pii/B9780123877383000044 |url-status=live }}</ref> Different other ''in-vitro'' biological activities of thujaplicins have been studied, such as insecticidal, anti-browning, anti-viral, anti-bacterial, anti-fungal, anti-proliferative and anti-oxidant.<ref>{{cite journal |last1=Saniewski |first1=Marian |last2=Horbowicz |first2=Marcin |last3=Kanlayanarat |first3=Sirichai |title=The Biological Activities of Troponoids and Their Use in Agriculture A Review |journal=Journal of Horticultural Research |date=10 September 2014 |volume=22 |issue=1 |pages=5–19 |doi=10.2478/johr-2014-0001|s2cid=33834249 |doi-access=free }}</ref><ref>{{cite journal |last1=Bentley |first1=Ronald |title=A fresh look at natural tropolonoids |journal=Nat. Prod. Rep. |date=2008 |volume=25 |issue=1 |pages=118–138 |doi=10.1039/b711474e|pmid=18250899 }}</ref>
*] are especially found in the hardwood and the bark.<ref name="Sjöström-2013" /> The most well-known wood phenolic constituents are ] (e.g. ]), ] (e.g. ], conidendrin, ], ]), norlignans (e.g. ], puerosides A and B, hydroxysugiresinol, sequirin-C), ]s (e.g. ], ]), ]s (e.g. ], ], ], ]). Most of the phenolic compounds have fungicidal properties and protect the wood from ].<ref name="Sjöström-2013" /> Together with the neolignans the phenolic compounds influence on the color of the wood. Resin acids and phenolic compounds are the main toxic contaminants present in the untreated ]s from ].<ref name="Ek-2009" /> ] compounds are one of the most abundant biomolecules produced by plants, such as ]s and ]s. Tannins are used in ] industry and have shown to exhibit different biological activities.<ref name="Hon-2001" /> ]s are very diverse, widely distributed in the ] kingdom and have numerous biological activities and roles.<ref name="Sjöström-2013" />


==Uses== ==Uses==
]
]

=== Production ===
{{Main|Forestry}}
Global production of roundwood rose from 3.5 billion m''³'' in 2000 to 4 billion m''³'' in 2021. In 2021, wood fuel was the main product with a 49 percent share of the total (2 billion m''³''), followed by coniferous industrial roundwood with 30 percent (1.2 billion m''³'') and non-coniferous industrial roundwood with 21 percent (0.9 billion m''³''). Asia and the Americas are the two main producing regions, accounting for 29 and 28 percent of the total roundwood production, respectively; Africa and Europe have similar shares of 20–21 percent, while Oceania produces the remaining 2 percent.<ref name="FAO-2023">{{Cite book |url=http://www.fao.org/documents/card/en/c/cc8166en |title=World Food and Agriculture – Statistical Yearbook 2023 |date=2023-11-29 |publisher=FAO |isbn=978-92-5-138262-2 |language=en |doi=10.4060/cc8166en}}</ref>

===Fuel=== ===Fuel===
{{main|Wood fuel}} {{Main|Wood fuel}}
Wood has a long history of being used as fuel,<ref>{{Cite book|url=https://books.google.com/books?id=jFvrF4DaZcgC&q=%C2%A0Wood+has+a+long+history+of+being+used+as+fuel&pg=PA261|title=Alternative Fuels and the Environment|last=Sterrett|first=Frances S.|date=1994-10-12|publisher=CRC Press|isbn=978-0-87371-978-0|language=en|df=mdy-all|access-date=October 6, 2020|archive-date=December 30, 2023|archive-url=https://web.archive.org/web/20231230131945/https://books.google.com/books?id=jFvrF4DaZcgC&q=%C2%A0Wood+has+a+long+history+of+being+used+as+fuel&pg=PA261#v=snippet&q=%C2%A0Wood%20has%20a%20long%20history%20of%20being%20used%20as%20fuel&f=false|url-status=live}}</ref> 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.
Wood is burned as a fuel mostly in rural areas of the world. Hard wood is preferred over softwood because it creates less smoke and burns longer. Adding a woodstove or fireplace to a home adds ambiance and warmth.<ref></ref>

===Pulpwood===
Pulpwood is wood that is raised specifically for use in making paper.

===Construction=== ===Construction===
] ] (]).]]


], ], ], New York built in 1899 is made of and decorated in wood.<ref>" {{webarchive|url=https://web.archive.org/web/20081216233832/http://www.dykerheightscivicassociation.com/saittareport.pdf |date=December 16, 2008 }}",''DykerHeightsCivicAssociation.com''</ref>]]
Wood has been an important construction material since humans began building shelters, ]s and ]s. Nearly all boats were made out of wood till the late 19th century, and wood remains in common use today in boat construction. New domestic housing in many parts of the world today is commonly made from timber-framed construction. In buildings made of other materials, wood will still be found as a supporting material, especially in ] construction, in interior doors and their frames, and as exterior cladding. Wood to be used for construction work is commonly known as '']'' in ]. Elsewhere, ''lumber'' usually refers to felled trees, and the word for sawn planks ready for use is ''timber''.
]
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. ] in particular was used for this purpose as it resisted decay as long as it was kept wet (it also served for water pipe before the advent of more modern plumbing).


Wood to be used for construction work is commonly known as '']'' in North America. Elsewhere, ''lumber'' usually refers to felled trees, and the word for sawn planks ready for use is ''timber''.<ref>{{Cite book|url=https://books.google.com/books?id=jSiRAAAAQBAJ&q=%C2%A0Wood+to+be+used+for+construction+work+is+commonly+known+as+lumber+in+North+America&pg=SA7-PA15|title=Materials for Interior Environments|last=Binggeli|first=Corky|year=2013|publisher=John Wiley & Sons|isbn=978-1-118-42160-4|language=en|df=mdy-all|access-date=October 6, 2020|archive-date=December 30, 2023|archive-url=https://web.archive.org/web/20231230132013/https://books.google.com/books?id=jSiRAAAAQBAJ&q=%C2%A0Wood+to+be+used+for+construction+work+is+commonly+known+as+lumber+in+North+America&pg=SA7-PA15#v=snippet&q=%C2%A0Wood%20to%20be%20used%20for%20construction%20work%20is%20commonly%20known%20as%20lumber%20in%20North%20America&f=false|url-status=live}}</ref> In Medieval Europe ] was the wood of choice for all wood construction, including beams, walls, doors, and floors. Today a wider variety of woods is used: solid wood doors are often made from ], small-knotted ], and ].
Wood unsuitable for construction in its native form may be broken down mechanically (into fibres or chips) or chemically (into cellulose) and used as a raw material for other building materials such as ], ], ], ] (MDF), ] (OSB). Such wood derivatives are widely used: wood fibers are an important component of most ], and cellulose is used as a component of some ] materials. Wood derivatives can also be used for kinds of flooring, for example ].


], Russia are among a handful of ]s built entirely of wood, without metal joints. See ] for more details.]]
Wood is also used for cutlery, such as ], ]s, and other utensils, like the ].
New domestic housing in many parts of the world today is commonly made from timber-framed construction. ] 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.
<!-- Adding a "Pop culture" section here will result in an immediate block. -->

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

====Flooring====
].]]
{{Main |Wood flooring}}A solid wood floor is a floor laid with planks or battens created from a single piece of timber, usually a hardwood. Since wood is hydroscopic (it acquires and loses moisture from the ambient conditions around it) this potential instability effectively limits the length and width of the boards.

Solid hardwood flooring is usually cheaper than engineered timbers and damaged areas can be sanded down and refinished repeatedly, the number of times being limited only by the thickness of wood above the tongue.

Solid hardwood floors were originally used for structural purposes, being installed perpendicular to the wooden support beams of a building (the joists or bearers) and solid construction timber is still often used for sports floors as well as most traditional wood blocks, ]s and ].

====Engineered products====
{{main |Engineered wood}}

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.<ref name="apawood">{{cite web|url=http://www.apawood.org/pdfs/download_pdf.cfm?PDFFilename=managed/E30.pdf|title=APA – The Engineered Wood Association|work=apawood.org|url-status=live|archive-url=https://web.archive.org/web/20060627045932/http://www.apawood.org/pdfs/download_pdf.cfm?PDFFilename=managed%2FE30.pdf|archive-date=June 27, 2006|df=mdy-all}}</ref>

These products include ] (glulam), wood structural panels (including ], ] and composite panels), ] (LVL) and other structural composite lumber (SCL) products, ], and I-joists.<ref name="apawood" /> Approximately 100 million cubic meters of wood was consumed for this purpose in 1991.<ref name="Horst-2005"/> The trends suggest that particle board and fiber board will overtake plywood.

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 ], ], and ] (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 ]. Wood derivatives can be used for kinds of flooring, for example ].

===Furniture and utensils===
Wood has always been used extensively for ], such as ] and beds. It is also used for tool handles and cutlery, such as ], ]s, and other utensils, like the ] and ].

===Other===
Further developments include new ] glue applications, recyclable food packaging, rubber tire replacement applications, anti-bacterial medical agents, and high strength fabrics or composites.<ref>{{cite web|url=http://www.forintek.ca/public/pdf/annual%20report/AR_2007_2008/AR_ENG_2007.pdf|title=FPInnovations|work=forintek.ca|url-status=dead|archive-url=https://web.archive.org/web/20090319100903/http://www.forintek.ca/public/pdf/annual%20report/AR_2007_2008/AR_ENG_2007.pdf|archive-date=March 19, 2009|df=mdy-all}}</ref>
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. Moisture content electronic monitoring can also enhance next generation wood protection.<ref>"System for remotely monitoring moisture content on wooden elements" I Arakistain, O Munne EP Patent EPO1382108.0</ref>

===Art===
]'', ]]]
Wood has long been used as an ]. It has been used to make sculptures and ] for millennia. Examples include the ]s carved by North American indigenous people from conifer trunks, often Western Red Cedar ('']'').

Other uses of wood in the arts include:
* ] ] and ]
* Wood can be a surface to paint on, such as in ]
* Many ]s are made mostly or entirely of wood

===Sports and recreational equipment===
Many types of ] are made of wood, or were constructed of wood in the past. For example, ]s are typically made of ]. The ]s which are legal for use in ] are frequently made of ] or ], and in recent years have been constructed from ] even though that wood is somewhat more fragile. ] courts have been traditionally made out of ].

Many other types of sports and recreation equipment, such as ]s, ]s, ]s and ], were commonly made of wood in the past, but have since been replaced with more modern materials such as aluminium, ] or ]s such as ] and ]. One noteworthy example of this trend is the family of ] commonly known as the '']'', the heads of which were traditionally made of ] wood in the early days of the game of golf, but are now generally made of metal or (especially in the case of ]) carbon-fiber composites.

==Bacterial degradation==
Little is known about the bacteria that degrade cellulose. ] in '']'' may play a role in the degradation of sunken wood. '']'', '']'', '']'', '']'', and '']'' have been detected in wood submerged for over a year.<ref>{{cite journal|title=How Deep-Sea Wood Falls Sustain Chemosynthetic Life|author1=Christina Bienhold|author2=Petra Pop Ristova|author3=Frank Wenzhöfer|author4=Thorsten Dittmar|author5=Antje Boetius|journal=PLOS ONE|volume = 8|issue=1|pages=e53590|date=January 2, 2013|df=mdy-all|doi=10.1371/journal.pone.0053590|pmid=23301092|pmc=3534711|bibcode = 2013PLoSO...853590B|doi-access=free}}</ref>
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==See also== ==See also==
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==References==
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{{Commonscat|Wood}}
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{{wiktionary}}
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===General=== ==Sources==
{{Free-content attribution
* {{cite book
| title = World Food and Agriculture – Statistical Yearbook 2023
|authorlink=R. Bruce Hoadley
| author =
|last=Hoadley
| publisher = FAO
|first=R. Bruce
| documentURL = https://www.fao.org/documents/card/en?details=cc8166en
|date=2000
| license statement URL = https://commons.wikimedia.org/File:World_Food_and_Agriculture_-_Statistical_Yearbook_2023.pdf <!-- Also in the document itself -->
|title=Understanding Wood: A Craftsman’s Guide to Wood Technology
| license = CC BY-SA IGO 3.0
|publisher=]
|isbn=1-56158-358-8
}} }}
* Shigo, Alex. (1986) ''A New Tree Biology Dictionary''. Shigo and Trees, Associates. ISBN 0-943563-12-7
*


==References==
{{reflist|30em}}
* {{cite book |author-link = R. Bruce Hoadley |last = Hoadley |first = R. Bruce |date = 2000 |title = Understanding Wood: A Craftsman's Guide to Wood Technology |publisher = ] |isbn = 978-1-56158-358-4 }}

==External links==
{{commons category}}
* (archived 27 May 2016)
* ({{Webarchive|url=https://web.archive.org/web/20150407062512/http://www.thewoodexplorer.com/ |date=April 7, 2015 }})
* (archived 14 April 2011)
{{Botany}} {{Botany}}
{{Forestry}}
{{Wood products}}
{{Woodworking}}
{{Natural resources}}
{{Tannin source}}
{{Sculptures}}
{{Authority control}}
{{Portal bar|Arthropods|Ecology|Engineering|Environment|Fungi|Islands|Painting|Trains|Trees}}


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Latest revision as of 14:50, 13 November 2024

Fibrous material from trees or other plants

For a small forest, see Woodland. For wood as a commodity, see Timber. For other uses, see Wood (disambiguation) and Wooden (disambiguation).

Wood samples  Pine   Spruce   Larch   Juniper   Aspen   Hornbeam   Birch   Alder   Beech   Oak   Elm   Cherry   Pear   Maple   Linden   Ash 

Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants. It is an organic material – a natural composite of cellulosic 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 mechanical-support function, enabling woody plants to grow large or to stand up by themselves. It also conveys water and nutrients among 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 fibers.

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.

Wood is scientifically studied and researched through the discipline of wood science, which was initiated since the beginning of the 20th century.

History

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

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

People have used wood for thousands of years for many purposes, including as a fuel or as a construction material for making houses, tools, weapons, furniture, packaging, artworks, and paper. Known constructions using wood date back ten thousand years. Buildings like the longhouses in Neolithic Europe were made primarily of wood.

Recent use of wood has been enhanced by the addition of steel and bronze into construction.

The year-to-year variation in tree-ring widths and isotopic abundances gives clues to the prevailing climate at the time a tree was cut.

Physical properties

Diagram of secondary growth in a tree showing idealized vertical and horizontal sections. A new layer of wood is added in each growing season, thickening the stem, existing branches and roots, to form a growth ring.

Growth rings

See also: Dendrochronology § Growth rings

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. These cells then go on to form thickened secondary cell walls, composed mainly of cellulose, hemicellulose and lignin.

Where the differences between the seasons are distinct, e.g. New Zealand, 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 the distinctiveness between seasons is annual (as is the case in equatorial regions, e.g. Singapore), these growth rings are referred to as annual rings. Where there is little seasonal difference growth rings are likely to be indistinct or absent. If the bark of the tree has been removed in a particular area, the rings will likely be deformed as the plant overgrows the scar.

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. There are major differences, depending on the kind of wood. 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. On the whole, as a tree gets larger in diameter the width of the growth rings decreases.

Knots

A knot on a tree trunk

As a tree grows, lower branches often die, and their bases may become overgrown and enclosed by subsequent layers of trunk wood, forming a type of imperfection known as a knot. The dead branch may not be attached to the trunk wood except at its base and can drop out after the tree has been sawn into boards. Knots affect the technical properties of the wood, usually reducing tension strength, 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.

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 in vertical section

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 when 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 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.

— Samuel J. Record, The Mechanical Properties of Wood

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 (knotting), 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

"Heartwood" redirects here. For other uses, see Heartwood (disambiguation). "Sapwood" redirects here. For the missile also called "SS-6 Sapwood", see R7 Semyorka. See also: Trunk (botany)
A section of a yew branch showing 27 annual growth rings, pale sapwood, dark heartwood, and pith (center dark spot). The dark radial lines are small knots.

Heartwood (or duramen) is wood that as a result of a naturally occurring chemical transformation has become more resistant to decay. Heartwood formation is a genetically programmed process that occurs spontaneously. Some uncertainty exists as to whether the wood dies during heartwood formation, as it can still chemically react to decay organisms, but only once.

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. Some others never form heartwood.

Heartwood is often visually distinct from the living sapwood and can be distinguished in a cross-section where the boundary will tend to follow the growth rings. For example, it is sometimes much darker. Other processes such as decay or insect invasion can also discolor wood, even in woody plants that do not form heartwood, which may lead to confusion.

Sapwood (or alburnum) is the younger, outermost wood; in the growing tree it is living wood, 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. 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 (12 in) or more in diameter, before any heartwood begins to form, for example, in second growth hickory, or open-grown pines.

Cross-section of an oak log showing growth rings

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 relatively 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 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.

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

The wood of coast redwood is distinctively red.

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 variation does not imply a significant difference in the mechanical properties of heartwood and sapwood, although there may be a marked biochemical difference between the two.

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, and very flammable. Tree 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.

Since the latewood of a growth ring is usually darker in color than the earlywood, this fact may be used in visually 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 often appear on a finished surface as darker than the denser latewood, though on cross sections of heartwood the reverse is commonly true. Otherwise 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. Ordinary sap-staining is due to fungal growth, but does not necessarily produce a weakening effect.

Water content

Water occurs in living wood in three locations, namely:

Equilibrium moisture content in wood.

In heartwood it occurs only in the first and last forms. Wood that is thoroughly air-dried (in equilibrium with the moisture content of the air) 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 occurs in the softening action of water on rawhide, paper, or cloth. Within certain limits, the greater the water content, the greater its softening effect. The moisture in wood can be measured by several different moisture meters.

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.

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

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

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

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. 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 localized 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 fibers are the elements which give strength and toughness to wood, while the vessels are a source of weakness.

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 alder, basswood, birch, buckeye, maple, willow, and the Populus species such as aspen, cottonwood and poplar. Some species, such as walnut and cherry, are on the border between the two classes, forming an intermediate group.

Earlywood and latewood

In softwood

Earlywood and latewood in a softwood; radial view, growth rings closely spaced in Rocky Mountain Douglas-fir

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 less latewood. 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, where strength or ease of working is essential, woods of moderate to slow growth should be chosen.

In ring-porous woods

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 six to ten 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."

The effect of rate of growth on the qualities of chestnut wood is summarized 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."

In diffuse-porous woods

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.

Monocots

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 resembles ordinary, "dicot" or conifer timber in its gross handling characteristics 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 and in the manufacture of engineered flooring, panels and veneer. Another major plant group that produces 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 processed raw material is quite different from ordinary wood.

Specific gravity

The single most revealing property of wood as an indicator of wood quality is specific gravity (Timell 1986), as both pulp yield and lumber strength are determined by it. Specific gravity is the ratio of the mass of a substance to the mass of an equal volume of water; density is the ratio of a mass of a quantity of a substance to the volume of that quantity and is expressed in mass per unit substance, e.g., grams per milliliter (g/cm or g/ml). The terms are essentially equivalent as long as the metric system is used. Upon drying, wood shrinks and its density increases. Minimum values are associated with green (water-saturated) wood and are referred to as basic specific gravity (Timell 1986).

The U.S. Forest Products Laboratory lists a variety of ways to define specific gravity (G) and density (ρ) for wood:

Symbol Mass basis Volume basis
G0 Ovendry Ovendry
Gb (basic) Ovendry Green
G12 Ovendry 12% MC
Gx Ovendry x% MC
ρ0 Ovendry Ovendry
ρ12 12% MC 12% MC
ρx x% MC x% MC

The FPL has adopted Gb and G12 for specific gravity, in accordance with the ASTM D2555 standard. These are scientifically useful, but don't represent any condition that could physically occur. The FPL Wood Handbook also provides formulas for approximately converting any of these measurements to any other.

Density

See also: Janka hardness test

Wood density is determined by multiple growth and physiological factors compounded into "one fairly easily measured wood characteristic" (Elliott 1970).

Age, diameter, height, radial (trunk) growth, geographical location, site and growing conditions, silvicultural treatment, and seed source all to some degree influence wood density. Variation is to be expected. Within an individual tree, the variation in wood density is often as great as or even greater than that between different trees (Timell 1986). Variation of specific gravity within the bole of a tree can occur in either the horizontal or vertical direction.

Because the specific gravity as defined above uses an unrealistic condition, woodworkers tend to use the "average dried weight", which is a density based on mass at 12% moisture content and volume at the same (ρ12). This condition occurs when the wood is at equilibrium moisture content with air at about 65% relative humidity and temperature at 30 °C (86 °F). This density is expressed in units of kg/m or lbs/ft.

Tables

The following tables list the mechanical properties of wood and lumber plant species, including bamboo. See also Mechanical properties of tonewoods for additional properties.

Wood properties:

Common name Scientific name Moisture content Density (kg/m) Compressive strength (megapascals) Flexural strength (megapascals)
Red Alder Alnus rubra Green 370 20.4 45
Red Alder Alnus rubra 12.00% 410 40.1 68
Black Ash Fraxinus nigra Green 450 15.9 41
Black Ash Fraxinus nigra 12.00% 490 41.2 87
Blue Ash Fraxinus quadrangulata Green 530 24.8 66
Blue Ash Fraxinus quadrangulata 12.00% 580 48.1 95
Green Ash Fraxinus pennsylvanica Green 530 29 66
Green Ash Fraxinus pennsylvanica 12.00% 560 48.8 97
Oregon Ash Fraxinus latifolia Green 500 24.2 52
Oregon Ash Fraxinus latifolia 12.00% 550 41.6 88
White Ash Fraxinus americana Green 550 27.5 66
White Ash Fraxinus americana 12.00% 600 51.1 103
Bigtooth Aspen Populus grandidentata Green 360 17.2 37
Bigtooth Aspen Populus grandidentata 12.00% 390 36.5 63
Quaking Aspen Populus tremuloides Green 350 14.8 35
Quaking Aspen Populus tremuloides 12.00% 380 29.3 58
American Basswood Tilia americana Green 320 15.3 34
American Basswood Tilia americana 12.00% 370 32.6 60
American Beech Fagus grandifolia Green 560 24.5 59
American Beech Fagus grandifolia 12.00% 640 50.3 103
Paper Birch Betula papyrifera Green 480 16.3 44
Paper Birch Betula papyrifera 12.00% 550 39.2 85
Sweet Birch Betula lenta Green 600 25.8 65
Sweet Birch Betula lenta 12.00% 650 58.9 117
Yellow Birch Betula alleghaniensis Green 550 23.3 57
Yellow Birch Betula alleghaniensis 12.00% 620 56.3 114
Butternut Juglans cinerea Green 360 16.7 37
Butternut Juglans cinerea 12.00% 380 36.2 56
Black Cherry Prunus serotina Green 470 24.4 55
Blach Cherry Prunus serotina 12.00% 500 49 85
American Chestnut Castanea dentata Green 400 17 39
American Chestnut Castanea dentata 12.00% 430 36.7 59
Balsam Poplar Cottonwood Populus balsamifera Green 310 11.7 27
Balsam Poplar Cottonwood Populus balsamifera 12.00% 340 27.7 47
Black Cottonwood Populus trichocarpa Green 310 15.2 34
Black Cottonwood Populus trichocarpa 12.00% 350 31 59
Eastern Cottonwood Populus deltoides Green 370 15.7 37
Eastern Cottonwood Populus deltoides 12.00% 400 33.9 59
American Elm Ulmus americana Green 460 20.1 50
American Elm Ulmus americana 12.00% 500 38.1 81
Rock Elm Ulmus thomasii Green 570 26.1 66
Rock Elm Ulmus thomasii 12.00% 630 48.6 102
Slippery Elm Ulmus rubra Green 480 22.9 55
Slippery Elm Ulmus rubra 12.00% 530 43.9 90
Hackberry Celtis occidentalis Green 490 18.3 45
Hackberry Celtis occidentalis 12.00% 530 37.5 76
Bitternut Hickory Carya cordiformis Green 600 31.5 71
Bitternut Hickory Carya cordiformis 12.00% 660 62.3 118
Nutmeg Hickory Carya myristiciformis Green 560 27.4 63
Nutmeg Hickory Carya myristiciformis 12.00% 600 47.6 114
Pecan Hickory Carya illinoinensis Green 600 27.5 68
Pecan Hickory Carya illinoinensis 12.00% 660 54.1 94
Water Hickory Carya aquatica Green 610 32.1 74
Water Hickory Carya aquatica 12.00% 620 59.3 123
Mockernut Hickory Carya tomentosa Green 640 30.9 77
Mockernut Hickory Carya tomentosa 12.00% 720 61.6 132
Pignut Hickory Carya glabra Green 660 33.2 81
Pignut Hickory Carya glabra 12.00% 750 63.4 139
Shagbark Hickory Carya ovata Green 640 31.6 76
Shagbark Hickory Carya ovata 12.00% 720 63.5 139
Shellbark Hickory Carya laciniosa Green 620 27 72
Shellbark Hickory Carya laciniosa 12.00% 690 55.2 125
Honeylocust Gleditsia triacanthos Green 600 30.5 70
Honeylocust Gleditsia triacanthos 12.00% 600 51.7 101
Black Locust Robinia pseudoacacia Green 660 46.9 95
Black Locust Robinia pseudoacacia 12.00% 690 70.2 134
Cucumber Tree Magnolia Magnolia acuminata Green 440 21.6 51
Cucumber Tree Magnolia Magnolia acuminata 12.00% 480 43.5 85
Southern Magnolia Magnolia grandiflora Green 460 18.6 47
Southern Magnolia Magnolia grandiflora 12.00% 500 37.6 77
Bigleaf Maple Acer macrophyllum Green 440 22.3 51
Bigleaf Maple Acer macrophyllum 12.00% 480 41 74
Black Maple Acer nigrum Green 520 22.5 54
Black Maple Acer nigrum 12.00% 570 46.1 92
Red Maple Acer rubrum Green 490 22.6 53
Red Maple Acer rubrum 12.00% 540 45.1 92
Silver Maple Acer saccharinum Green 440 17.2 40
Silver Maple Acer saccharinum 12.00% 470 36 61
Sugar Maple Acer saccharum Green 560 27.7 65
Sugar Maple Acer saccharum 12.00% 630 54 109
Black Red Oak Quercus velutina Green 560 23.9 57
Black Red Oak Quercus velutina 12.00% 610 45 96
Cherrybark Red Oak Quercus pagoda Green 610 31.9 74
Cherrybark Red Oak Quercus pagoda 12.00% 680 60.3 125
Laurel Red Oak Quercus hemisphaerica Green 560 21.9 54
Laurel Red Oak Quercus hemisphaerica 12.00% 630 48.1 87
Northern Red Oak Quercus rubra Green 560 23.7 57
Northern Red Oak Quercus rubra 12.00% 630 46.6 99
Pin Red Oak Quercus palustris Green 580 25.4 57
Pin Red Oak Quercus palustris 12.00% 630 47 97
Scarlet Red Oak Quercus coccinea Green 600 28.2 72
Scarlet Red Oak Quercus coccinea 12.00% 670 57.4 120
Southern Red Oak Quercus falcata Green 520 20.9 48
Southern Red Oak Quercus falcata 12.00% 590 42 75
Water Red Oak Quercus nigra Green 560 25.8 61
Water Red Oak Quercus nigra 12.00% 630 46.7 106
Willow Red Oak Quercus phellos Green 560 20.7 51
Willow Red Oak Quercus phellos 12.00% 690 48.5 100
Bur White Oak Quercus macrocarpa Green 580 22.7 50
Bur White Oak Quercus macrocarpa 12.00% 640 41.8 71
Chestnut White Oak Quercus montana Green 570 24.3 55
Chestnut White Oak Quercus montana 12.00% 660 47.1 92
Live White Oak Quercus virginiana Green 800 37.4 82
Live White Oak Quercus virginiana 12.00% 880 61.4 127
Overcup White Oak Quercus lyrata Green 570 23.2 55
Overcup White Oak Quercus lyrata 12.00% 630 42.7 87
Post White Oak Quercus stellata Green 600 24 56
Post White Oak Quercus stellata 12.00% 670 45.3 91
Swamp Chestnut White Oak Quercus michauxii Green 600 24.4 59
Swamp Chestnut White Oak Quercus michauxii 12.00% 670 50.1 96
Swamp White Oak Quercus bicolor Green 640 30.1 68
Swamp White Oak Quercus bicolor 12.00% 720 59.3 122
White Oak Quercus alba Green 600 24.5 57
White Oak Quercus alba 12.00% 680 51.3 105
Sassafras Sassafras albidum Green 420 18.8 41
Sassafras Sassafras albidum 12.00% 460 32.8 62
Sweetgum Liquidambar styraciflua Green 460 21 49
Sweetgum Liquidambar styraciflua 12.00% 520 43.6 86
American Sycamore Platanus occidentalis Green 460 20.1 45
American Sycamore Platanus occidentalis 12.00% 490 37.1 69
Tanoak Notholithocarpus densiflorus Green 580 32.1 72
Tanoak Notholithocarpus densiflorus 12.00% 580 32.1 72
Black Tupelo Nyssa sylvatica Green 460 21 48
Black Tupelo Nyssa sylvatica 12.00% 500 38.1 66
Water Tupelo Nyssa aquatica Green 460 23.2 50
Water Tupelo Nyssa aquatica 12.00% 500 40.8 66
Black Walnut Juglans nigra Green 510 29.6 66
Black Walnut Juglans nigra 12.00% 550 52.3 101
Black Willow Salix nigra Green 360 14.1 33
Black Willow Salix nigra 12.00% 390 28.3 54
Yellow Poplar Liriodendron tulipifera Green 400 18.3 41
Yellow Poplar Liriodendron tulipifera 12.00% 420 38.2 70
Baldcypress Taxodium distichum Green 420 24.7 46
Baldcypress Taxodium distichum 12.00% 460 43.9 73
Atlantic White Cedar Chamaecyparis thyoides Green 310 16.5 32
Atlantic White Cedar Chamaecyparis thyoides 12.00% 320 32.4 47
Eastern Redcedar Juniperus virginiana Green 440 24.6 48
Eastern Redcedar Juniperus virginiana 12.00% 470 41.5 61
Incense Cedar Calocedrus decurrens Green 350 21.7 43
Incense Cedar Calocedrus decurrens 12.00% 370 35.9 55
Northern White Cedar Thuja occidentalis Green 290 13.7 29
Northern White Cedar Thuja occidentalis 12.00% 310 27.3 45
Port Orford Cedar Chamaecyparis lawsoniana Green 390 21.6 45
Port Orford Cedar Chamaecyparis lawsoniana 12.00% 430 43.1 88
Western Redcedar Thuja plicata Green 310 19.1 35.9
Western Redcedar Thuja plicata 12.00% 320 31.4 51.7
Yellow Cedar Cupressus nootkatensis Green 420 21 44
Yellow Cedar Cupressus nootkatensis 12.00% 440 43.5 77
Coast Douglas Fir Pseudotsuga menziesii var. menziesii Green 450 26.1 53
Coast Douglas Fir Pseudotsuga menziesii var. menziesii 12.00% 480 49.9 85
Interior West Douglas Fir Pseudotsuga Menziesii Green 460 26.7 53
Interior West Douglas Fir Pseudotsuga Menziesii 12.00% 500 51.2 87
Interior North Douglas Fir Pseudotsuga menziesii var. glauca Green 450 23.9 51
Interior North Douglas Fir Pseudotsuga menziesii var. glauca 12.00% 480 47.6 90
Interior South Douglas Fir Pseudotsuga lindleyana Green 430 21.4 47
Interior South Douglas Fir Pseudotsuga lindleyana 12.00% 460 43 82
Balsam Fir Abies balsamea Green 330 18.1 38
Balsam Fir Abies balsamea 12.00% 350 36.4 63
California Red Fir Abies magnifica Green 360 19 40
California Red Fir Abies magnifica 12.00% 380 37.6 72.4
Grand Fir Abies grandis Green 350 20.3 40
Grand Fir Abies grandis 12.00% 370 36.5 61.4
Noble Fir Abies procera Green 370 20.8 43
Noble Fir Abies procera 12.00% 390 42.1 74
Pacific Silver Fir Abies amabilis Green 400 21.6 44
Pacific Silver Fir Abies amabilis 12.00% 430 44.2 75
Subalpine Fir Abies lasiocarpa Green 310 15.9 34
Subalpine Fir Abies lasiocarpa 12.00% 320 33.5 59
White Fir Abies concolor Green 370 20 41
White Fir Abies concolor 12.00% 390 40 68
Eastern Hemlock Tsuga canadensis Green 380 21.2 44
Eastern Hemlock Tsuga canadensis 12.00% 400 37.3 61
Mountain Hemlock Tsuga mertensiana Green 420 19.9 43
Mountain Hemlock Tsuga mertensiana 12.00% 450 44.4 79
Western Hemlock Tsuga heterophylla Green 420 23.2 46
Western Hemlock Tsuga heterophylla 12.00% 450 49 78
Western Larch Larix occidentalis Green 480 25.9 53
Western Larch Larix occidentalis 12.00% 520 52.5 90
Eastern White Pine Pinus strobus Green 340 16.8 34
Eastern White Pine Pinus strobus 12.00% 350 33.1 59
Jack Pine Pinus banksiana Green 400 20.3 41
Jack Pine Pinus banksiana 12.00% 430 39 68
Loblolly Pine Pinus taeda Green 470 24.2 50
Loblolly Pine Pinus taeda 12.00% 510 49.2 88
Lodgepole Pine Pinus contorta Green 380 18 38
Lodgepole Pine Pinus contorta 12.00% 410 37 65
Longleaf Pine Pinus palustris Green 540 29.8 59
Longleaf Pine Pinus palustris 12.00% 590 58.4 100
Pitch Pine Pinus rigida Green 470 20.3 47
Pitch Pine Pinus rigida 12.00% 520 41 74
Pond Pine Pinus serotina Green 510 25.2 51
Pond Pine Pinus serotina 12.00% 560 52 80
Ponderosa Pine Pinus ponderosa Green 380 16.9 35
Ponderosa Pine Pinus ponderosa 12.00% 400 36.7 65
Red Pine Pinus resinosa Green 410 18.8 40
Red Pine Pinus resinosa 12.00% 460 41.9 76
Sand Pine Pinus clausa Green 460 23.7 52
Sand Pine Pinus clausa 12.00% 480 47.7 80
Shortleaf Pine Pinus echinata Green 470 24.3 51
Shortleaf Pine Pinus echinata 12.00% 510 50.1 90
Slash Pine Pinus elliottii Green 540 26.3 60
Slash Pine Pinus elliottii 12.00% 590 56.1 112
Spruce Pine Pinus glabra Green 410 19.6 41
Spruce Pine Pinus glabra 12.00% 440 39 72
Sugar Pine Pinus lambertiana Green 340 17 34
Sugar Pine Pinus lambertiana 12.00% 360 30.8 57
Virginia Pine Pinus virginiana Green 450 23.6 50
Virginia Pine Pinus virginiana 12.00% 480 46.3 90
Western White Pine Pinus monticola Green 360 16.8 32
Western White Pine Pinus monticola 12.00% 380 34.7 67
Redwood Old Growth Sequoia sempervirens Green 380 29 52
Redwood Old Growth Sequoia sempervirens 12.00% 400 42.4 69
Redwood New Growth Sequoia sempervirens Green 340 21.4 41
Redwood New Growth Sequoia sempervirens 12.00% 350 36 54
Black Spruce Picea mariana Green 380 19.6 42
Black Spruce Picea mariana 12.00% 460 41.1 74
Engelmann Spruce Picea engelmannii Green 330 15 32
Engelmann Spruce Picea engelmannii 12.00% 350 30.9 64
Red Spruce Picea rubens Green 370 18.8 41
Red Spruce Picea rubens 12.00% 400 38.2 74
Sitka Spruce Picea sitchensis Green 330 16.2 34
Sitka Spruce Picea sitchensis 12.00% 360 35.7 65
White Spruce Picea glauca Green 370 17.7 39
White Spruce Picea glauca 12.00% 400 37.7 68
Tamarack Spruce Larix laricina Green 490 24 50
Tamarack Spruce Larix laricina 12.00% 530 49.4 80

Bamboo properties:

Common name Scientific name Moisture content Density (kg/m) Compressive strength (megapascals) Flexural strength (megapascals)
Balku bans Bambusa balcooa green 45 73.7
Balku bans Bambusa balcooa air dry 54.15 81.1
Balku bans Bambusa balcooa 8.5 820 69 151
Indian thorny bamboo Bambusa bambos 9.5 710 61 143
Indian thorny bamboo Bambusa bambos 43.05 37.15
Nodding Bamboo Bambusa nutans 8 890 75 52.9
Nodding Bamboo Bambusa nutans 87 46 52.4
Nodding Bamboo Bambusa nutans 12 85 67.5
Nodding Bamboo Bambusa nutans 88.3 44.7 88
Nodding Bamboo Bambusa nutans 14 47.9 216
Clumping Bamboo Bambusa pervariabilis 45.8
Clumping Bamboo Bambusa pervariabilis 5 79 80
Clumping Bamboo Bambusa pervariabilis 20 35 37
Burmese bamboo Bambusa polymorpha 95.1 32.1 28.3
Bambusa spinosa air dry 57 51.77
Indian timber bamboo Bambusa tulda 73.6 40.7 51.1
Indian timber bamboo Bambusa tulda 11.9 68 66.7
Indian timber bamboo Bambusa tulda 8.6 910 79 194
dragon bamboo Dendrocalamus giganteus 8 740 70 193
Hamilton's bamboo Dendrocalamus hamiltonii 8.5 590 70 89
White bamboo Dendrocalamus membranaceus 102 40.5 26.3
String Bamboo Gigantochloa apus 54.3 24.1 102
String Bamboo Gigantochloa apus 15.1 37.95 87.5
Java Black Bamboo Gigantochloa atroviolacea 54 23.8 92.3
Java Black Bamboo Gigantochloa atroviolacea 15 35.7 94.1
Giant Atter Gigantochloa atter 72.3 26.4 98
Giant Atter Gigantochloa atter 14.4 31.95 122.7
Gigantochloa macrostachya 8 960 71 154
American Narrow-Leaved Bamboo Guadua angustifolia 42 53.5
American Narrow-Leaved Bamboo Guadua angustifolia 63.6 144.8
American Narrow-Leaved Bamboo Guadua angustifolia 86.3 46
American Narrow-Leaved Bamboo Guadua angustifolia 77.5 82
American Narrow-Leaved Bamboo Guadua angustifolia 15 56 87
American Narrow-Leaved Bamboo Guadua angustifolia 63.3
American Narrow-Leaved Bamboo Guadua angustifolia 28
American Narrow-Leaved Bamboo Guadua angustifolia 56.2
American Narrow-Leaved Bamboo Guadua angustifolia 38
Berry Bamboo Melocanna baccifera 12.8 69.9 57.6
Japanese timber bamboo Phyllostachys bambusoides 51
Japanese timber bamboo Phyllostachys bambusoides 8 730 63
Japanese timber bamboo Phyllostachys bambusoides 64 44
Japanese timber bamboo Phyllostachys bambusoides 61 40
Japanese timber bamboo Phyllostachys bambusoides 9 71
Japanese timber bamboo Phyllostachys bambusoides 9 74
Japanese timber bamboo Phyllostachys bambusoides 12 54
Tortoise shell bamboo Phyllostachys edulis 44.6
Tortoise shell bamboo Phyllostachys edulis 75 67
Tortoise shell bamboo Phyllostachys edulis 15 71
Tortoise shell bamboo Phyllostachys edulis 6 108
Tortoise shell bamboo Phyllostachys edulis 0.2 147
Tortoise shell bamboo Phyllostachys edulis 5 117 51
Tortoise shell bamboo Phyllostachys edulis 30 44 55
Tortoise shell bamboo Phyllostachys edulis 12.5 603 60.3
Tortoise shell bamboo Phyllostachys edulis 10.3 530 83
Early Bamboo Phyllostachys praecox 28.5 827 79.3
Oliveri Thyrsostachys oliveri 53 46.9 61.9
Oliveri Thyrsostachys oliveri 7.8 58 90

Hard versus soft

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.

There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it, at least for certain species. For example, in loblolly pine, wind exposure and stem position greatly affect the hardness of wood, as well as compression wood content. 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.

Chemistry

Chemical structure of lignin, which makes up about 25% of wood dry matter and is responsible for many of its properties.

The chemical composition of wood varies from species to species, but is approximately 50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other elements (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by weight. Wood also contains sulfur, chlorine, silicon, phosphorus, and other elements in small quantity.

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.

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.

Extractives

Aside from the structural polymers, i.e. cellulose, hemicellulose and lignin (lignocellulose), wood contains a large variety of non-structural constituents, composed of low molecular weight organic compounds, called extractives. These compounds are present in the extracellular space and can be extracted from the wood using different neutral solvents, such as acetone. Analogous content is present in the so-called exudate produced by trees in response to mechanical damage or after being attacked by insects or fungi. Unlike the structural constituents, the composition of extractives varies over wide ranges and depends on many factors. The amount and composition of extractives differs between tree species, various parts of the same tree, and depends on genetic factors and growth conditions, such as climate and geography. For example, slower growing trees and higher parts of trees have higher content of extractives. Generally, the softwood is richer in extractives than the hardwood. Their concentration increases from the cambium to the pith. Barks and branches also contain extractives. Although extractives represent a small fraction of the wood content, usually less than 10%, they are extraordinarily diverse and thus characterize the chemistry of the wood species. Most extractives are secondary metabolites and some of them serve as precursors to other chemicals. Wood extractives display different activities, some of them are produced in response to wounds, and some of them participate in natural defense against insects and fungi.

Forchem tall oil refinery in Rauma, Finland

These compounds contribute to various physical and chemical properties of the wood, such as wood color, fragnance, durability, acoustic properties, hygroscopicity, adhesion, and drying. Considering these impacts, wood extractives also affect the properties of pulp and paper, and importantly cause many problems in paper industry. Some extractives are surface-active substances and unavoidably affect the surface properties of paper, such as water adsorption, friction and strength. Lipophilic extractives often give rise to sticky deposits during kraft pulping and may leave spots on paper. Extractives also account for paper smell, which is important when making food contact materials.

Most wood extractives are lipophilic and only a little part is water-soluble. The lipophilic portion of extractives, which is collectively referred as wood resin, contains fats and fatty acids, sterols and steryl esters, terpenes, terpenoids, resin acids, and waxes. The heating of resin, i.e. distillation, vaporizes the volatile terpenes and leaves the solid component – rosin. The concentrated liquid of volatile compounds extracted during steam distillation is called essential oil. Distillation of oleoresin obtained from many pines provides rosin and turpentine.

Most extractives can be categorized into three groups: aliphatic compounds, terpenes and phenolic compounds. The latter are more water-soluble and usually are absent in the resin.

Uses

Main global producers of roundwood by type.
World production of roundwood by type

Production

Main article: Forestry

Global production of roundwood rose from 3.5 billion m³ in 2000 to 4 billion m³ in 2021. In 2021, wood fuel was the main product with a 49 percent share of the total (2 billion m³), followed by coniferous industrial roundwood with 30 percent (1.2 billion m³) and non-coniferous industrial roundwood with 21 percent (0.9 billion m³). Asia and the Americas are the two main producing regions, accounting for 29 and 28 percent of the total roundwood production, respectively; Africa and Europe have similar shares of 20–21 percent, while Oceania produces the remaining 2 percent.

Fuel

Main article: Wood fuel

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.

Pulpwood

Pulpwood is wood that is raised specifically for use in making paper.

Construction

The Saitta House, Dyker Heights, Brooklyn, New York built in 1899 is made of and decorated in wood.
Map of importers and exporters of forest products including wood in 2021

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. Elm in particular was used for this purpose as it resisted decay as long as it was kept wet (it also served for water pipe before the advent of more modern plumbing).

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. In Medieval Europe oak was the wood of choice for all wood construction, including beams, walls, doors, and floors. Today a wider variety of woods is used: solid wood doors are often made from poplar, small-knotted pine, and Douglas fir.

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.

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 mold into which concrete is poured during reinforced concrete construction.

Flooring

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

A solid wood floor is a floor laid with planks or battens created from a single piece of timber, usually a hardwood. Since wood is hydroscopic (it acquires and loses moisture from the ambient conditions around it) this potential instability effectively limits the length and width of the boards.

Solid hardwood flooring is usually cheaper than engineered timbers and damaged areas can be sanded down and refinished repeatedly, the number of times being limited only by the thickness of wood above the tongue.

Solid hardwood floors were originally used for structural purposes, being installed perpendicular to the wooden support beams of a building (the joists or bearers) and solid construction timber is still often used for sports floors as well as most traditional wood blocks, mosaics and parquetry.

Engineered products

Main article: Engineered wood

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.

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. Approximately 100 million cubic meters of wood was consumed for this purpose in 1991. The trends suggest that particle board and fiber board will overtake plywood.

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 be used for kinds of flooring, for example laminate flooring.

Furniture and utensils

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

Other

Further developments include new lignin glue applications, recyclable food packaging, rubber tire replacement applications, anti-bacterial medical agents, and high strength fabrics or composites. 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. Moisture content electronic monitoring can also enhance next generation wood protection.

Art

Prayer Bead with the Adoration of the Magi and the Crucifixion, Gothic boxwood miniature

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).

Other uses of wood in the arts include:

Sports and recreational equipment

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. National Basketball Association courts have been traditionally made out of parquetry.

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, titanium or composite materials such as fiberglass and carbon fiber. One noteworthy example of this trend is the family of golf clubs commonly known as the woods, the heads of which were traditionally made of persimmon wood in the early days of the game of golf, but are now generally made of metal or (especially in the case of drivers) carbon-fiber composites.

Bacterial degradation

Little is known about the bacteria that degrade cellulose. Symbiotic bacteria in Xylophaga may play a role in the degradation of sunken wood. Alphaproteobacteria, Flavobacteria, Actinomycetota, Clostridia, and Bacteroidota have been detected in wood submerged for over a year.

See also

Sources

 This article incorporates text from a free content work. Licensed under CC BY-SA IGO 3.0 (license statement/permission). Text taken from World Food and Agriculture – Statistical Yearbook 2023​, FAO.

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