Wood

Resources

Wood is the hard, tough, fibrous substance found beneath the bark in trees, shrubs, and other similar plants. Its principle physical properties include strength, stiffness, hardness, and density. For instance, the strength of wood can vary depending on the type of wood, along with such things as age, dryness, compression, and grain direction; while the density of wood indicates its degree of hardness (where the most dense woods are the harder ones).

The United States imports over 1.5 million tons and exports over 9.5 million tons of wood each year. With about one-third of the U.S. land covered by forests (about 302 million hectacres [746 million acres]), the United States exports much more wood than it imports. According to the U.S. Department of Agriculture (USDA), the cutting of timber (wood) is the largest use of land in the United States. Alaska, California, and Oregon contain the most forested lands in the United States. However, Georgia, Oregon, and Montana contain the most timberland; that is, land able to be used to produce industrial woods. Seventy-one percent of all timberland is privately owned, while the other 29% is publicly owned.

Also known as secondary xylem, wood is a composite of tissues found in trees. Secondary xylem is composed primarily of cells, called vessel elements in angiosperms, or of slightly different cells in gymnosperms called tracheids. These cells of secondary xylem, along with specialized cells of a type called parenchyma, are made by a meristematic tissue called the vascular cambium. As the vascular cambium generates new cells, secondary xylem accumulates on its inside, and the tree increases in diameter.

Newly made vessel elements and tracheids are water conduits from the roots of plants to their leaves. When first made, vessel elements and tracheids are alive but once they mature and become functional, they die. The functional vessel elements or tracheids occur in a few cell layers behind the vascular cambium, in a water-conducting section of the secondary xylem known as sapwood.

The parenchyma are made by the vascular cambium along with the vessels or tracheids, and are located at certain points along the perimeter of the vascular cambium. As the tree expands through growth, these narrow columns of parenchyma cells, called xylem rays, become longer, and ultimately extend from the vascular cambium to very near the center of the tree trunk. The function of xylem rays is to transfer aqueous material horizontally along the diameter of the tree, at a right angle to the flow of water in vessel elements and tracheids. The parenchyma cells of the xylem rays are alive in their mature, functional state.

As newer vessel elements or tracheids are made, older ones become buried under successive layers of more recently formed xylem. As the tree gets progressively larger in diameter, older secondary xylem tissues no longer conduct water. After this happens, these non-conducting cells are used to store waste products, such as resins. The xylem rays function to conduct wastes from actively functioning cells near the vascular cambium, to the non-functioning xylem cells. This waste-filled secondary xylem is called heartwood. By the time that a tree is larger than about 4 to 8 in (10 to 20 cm) in diameter, most of its biomass is composed of heartwood. New sapwood is created during each growing season. However, within two to three years these cells become part of the heartwood. It is the heartwood of trees that is harvested to manufacture the lumber and paper used by people.

Wood of different species varies in density and strength, due to the size and density of the vessel elements or tracheids in the secondary xylem. For example, heartwood of the Brazilian ironwood (Caesalpinia ferrea) has very tiny vessel elements and is extremely dense. At the opposite extreme, the heartwood of balsa (Ochroma pyramidale) has very large vessel elements, and is correspondingly light in density. The wood of typical gymnosperms is generally soft and light in density, because tracheids do not fit together as closely as the vessel elements in the xylem of most angiosperms.

The size of tracheids and vessel elements also varies within a single tree, according to the season of the year that they were laid down during growth. In spring, when air temperatures are cool and soil moisture is typically plentiful, the vascular cambium of trees makes large diameter xylem cells. As the moisture wanes and temperatures increase in the summer, the vascular cambium makes smaller diameter cells. In the winter, no new cells are made, because of the cold temperatures. This cycle repeats itself every year and makes visible growth rings in the tree (except in the tropics). These rings are evident because spring wood, with larger diameter cells, is relatively dark in appearance, while summer wood is lighter in color. This annual repetition of differing cell sizes in growth rings is useful in ecological studies through dendro chronology. Because the size of vessel elements or tracheids is dependent on both air temperature and water, dendrochronologists can determine past periods of drought, flood, and unseasonal cold or heat, by studying variations in the width of growth rings.

Vessel elements and tracheids differ in length between angiosperms and gymnosperms. Although the length of individual cells makes little difference in the ability of trees to conduct water, the length of cells is of great importance to the paper industry. The length of these cells corresponds to the fiber length of pulp that is turned into paper, and influences the quality of paper that can be produced. Short fibers make fine grade papers, while longer fibers make coarser grade papers.

Some wood can be produced very quickly and, consequently, it is usually a cheap and easily renewed resource. Because of this feature, it is still used extensively as a fuel and a building material. Wood can be divided into two types, hard and soft wood. According to the USDA, around one-third of all U.S. timber removed were hardwoods, with the other two-thirds removed being softwoods. Each type has different physical properties.

Hardwood is very dense and strong, and it is much slower growing and, consequently, is more expensive than soft wood. Hardwoods are used where strength is needed. For example, the large wooden ships of the past were built of hardwood such as oak. Softwoods, such as that obtained from conifers, can be used where less physical strength is needed. They can be used in the manufacture of smaller structures or, as is more common, in the production of paper and pulp. Softwood, such as that obtained from conifers, is very quick to grow and, as such, it is relatively cheap and easily renewable.

Wood is a versatile, natural product. It can be used directly as a building material or fuel. With minor treatment, paper and pulp can be manufactured. With greater treatment, a number of commercially important compounds can be obtained. Different trees produce wood with different physical and chemical characteristics.

KEY TERMS

Meristem —A cluster of similar, undifferentiated dendrochronology plant cells that produce cells, which do differentiate and become mature tissues.

Parenchyma —A non-vascular tissue composed of large, thin-walled cells that may differ in size, shape, and structure of cell wall.

Tracheids —Thick walled, lignified elements of xylem that have no perforations on the crosswalls of adjoining cells. Instead, water is transferred among tracheid cells through holes in the side of the cell walls known as bordered pits.

Vascular cambium —Undifferentiated plant tissue that gives rise to phloem and xylem. Vessel elements—Thick-walled, lignified elements of xylem that have perforated or missing end walls. The relatively large openings in the crosswalls between adjoining cells allow a continuous, vertical transport of water.

Xylem —Plant tissue that transports water and minerals upward from the roots.

Resources

BOOKS

Bowyer, Jim L. Forest Products and Wood Science: An Introduction. Ames, IA: Iowa State Press, 2003.

Ennos, Roland. Trees. Washington, DC: Smithsonian Institution Press, 2001.

Hough, Romeyn Beck. The Wood Book. New York: Taschen, 2002.

Pakenham, Thomas. Remarkable Trees of the World. New York: Norton, 2002.

Tudge, Colin. The Tree: A Natural History of What Trees Are, How They Live, and Why They Matter. New York: Crown Publishers, 2006.

Stephen R. Johnson

Wood

Wood, also known as secondary xylem, is a composite of tissues found in trees. Secondary xylem is composed primarily of cells, called vessel elements in angiosperms, or of slightly different cells in gymnosperms called tracheids. These cells of secondary xylem, along with specialized cells of a type called parenchyma, are made by a meristematic tissue called the vascular cambium. As the vascular cambium generates new cells, secondary xylem accumulates on its inside, and the tree increases in diameter.

Newly made vessel elements and tracheids are water conduits from the roots of plants to their leaves. When first made, vessel elements and tracheids are alive but once they mature and become functional, they die. The functional vessel elements or tracheids occur in a few cell layers behind the vascular cambium, in a water-conducting section of the secondary xylem known as sapwood.

The parenchyma are made by the vascular cambium along with the vessels or tracheids, and are located at certain points along the perimeter of the vascular cambium. As the tree expands through growth, these narrow columns of parenchyma cells, called xylem rays, become longer, and ultimately extend from the vascular cambium to very near the center of the tree trunk. The function of xylem rays is to transfer aqueous material horizontally along the diameter of the tree, at a right angle to the flow of water in vessel elements and tracheids. The parenchyma cells of the xylem rays are alive in their mature, functional state.

As newer vessel elements or tracheids are made, older ones become buried under successive layers of more recently formed xylem. As the tree gets progressively larger in diameter, older secondary xylem tissues no longer conduct water. After this happens, these nonconducting cells are used to store waste products, such as resins . The xylem rays function to conduct wastes from actively functioning cells near the vascular cambium, to the non-functioning xylem cells. This waste-filled secondary xylem is called heartwood. By the time that a tree is larger than about 4-8 in (10-20 cm) in diameter, most of its biomass is composed of heartwood. New sapwood is created during each growing season but, within two to three years these cells become part of the heartwood. It is the heartwood of trees that is harvested to manufacture the lumber and paper used by people.

Wood of different species varies in density and strength, due to the size and density of the vessel elements or tracheids in the secondary xylem. For example, heartwood of the Brazilian ironwood (Caesalpinia ferrea) has very tiny vessel elements and is extremely dense. At the opposite extreme, the heartwood of balsa (Ochroma pyramidale) has very large vessel elements, and is correspondingly light in density. The wood of typical gymnosperms is generally soft and light in density, because tracheids do not fit together as closely as the vessel elements in the xylem of most angiosperms.

The size of tracheids and vessel elements also varies within a single tree, according to the season of the year that they were laid down during growth. In spring, when air temperatures are cool and soil moisture is typically plentiful, the vascular cambium of trees makes large diameter xylem cells. As the moisture wanes and temperatures increase in the summer, the vascular cambium makes smaller diameter cells. In the winter, no new cells are made, because of the cold temperatures. This cycle repeats itself every year and makes visible growth rings in the tree (except in the tropics). These rings are evident because spring wood, with larger diameter cells, is relatively dark in appearance, while summer wood is lighter in color . This annual repetition of differing cell sizes in growth rings is useful in ecological studies through dendrochronology. Because the size of vessel elements or tracheids is dependent on both air temperature and water, dendrochronologists can determine past periods of drought , flood, and unseasonal cold or heat , by studying variations in the width of growth rings.

Vessel elements and tracheids differ in length between angiosperms and gymnosperms. Although the length of individual cells makes little difference in the ability of trees to conduct water, the length of cells is of great importance to the paper industry. The length of these cells corresponds to the fiber length of pulp that is to turned into paper, and influences the quality of paper that can be produced. Short fibers make fine grade papers, while longer fibers make coarser grade papers.

Resources

books

Bell, P. R. Green Plants, Their Origin and Diversity. Portland: Dioscorides Press, 1992.

Fahn, A. Plant Anatomy. 5th ed. New York: Pergamon Press, 1990.

Lewington, A. Plants for People. New York: Oxford University Press, 1990.

Stephen R. Johnson

KEY TERMS

Meristem

—A cluster of similar, undifferentiated dendrochronology plant cells that produce cells which do differentiate, and become mature tissues.

Parenchyma

—A non-vascular tissue composed of large, thin-walled cells that may differ in size, shape, and structure of cell wall.

Tracheids

—Thick walled, lignified elements of xylem which have no perforations on the cross-walls of adjoining cells. Instead, water is transferred among tracheid cells through holes in the side of the cell walls known as bordered pits.

Vascular cambium

—Undifferentiated plant tissue which gives rise to phloem and xylem.

Vessel elements

—Thick-walled, lignified elements of xylem that have perforated or missing end walls. The relatively large openings in the cross-walls between adjoining cells allow a continuous, vertical transport of water.

Xylem

—Plant tissue that transports water and minerals upward from the roots.

WOOD

In Hebrew the word ʿeẓ (עֵץ) means both "tree" and "wood" (also "stick"). The Bible speaks of special craftsmen for woodworking, ḥarashei ʿeẓ, who worked in the various branches of wood manufacturing (Ex. 31:5; ii Sam. 5:11; i Chron. 22:15, et al.). The Bible also mentions several types of wood which were treated for various purposes; gopher wood (Gen. 6:14), cedar wood (Ezra 3:7; et al.), acacia wood (Ex. 38:1, et al.), juniper wood (בְּרוֹשׁ; i Kings 6:34), almug wood (i Kings 10:11), and olive wood (i Kings 6:31). Apparently, cedars and cypress trees were used primarily for the construction of ornate buildings, while the other types were used mainly in the construction of furniture, other articles, and utensils. Cedars and almug wood were imported from abroad, mainly during the period of the monarchy, while acacia and olive trees were common in Palestine.

The Bible mentions wooden handles and axes (Deut. 19:5), spear handles (ii Sam. 21:19), etc. Stone implements were attached to the wooden handles by tying them together with sinews or ropes, while metal blades of various shapes and having different uses were attached to wooden handles by tying them with cords, by driving one end into the wood, and by making a metal hole into which the wood was inserted and riveted. The Bible mentions a number of pieces of wooden furniture which were used in the Temple and the Tabernacle: the table of display (Ex. 25:23–30), the ark (Ex. 25:10–14), the altar for burnt offerings (Ex. 38:1), and the incense altar (Ex. 37:25). In connection with the laws of uncleanness and purification, the Bible mentions various wooden articles (Lev. 15:12). These are mainly various household utensils: mortars, dishes, spoons, etc. The number of wooden objects from the biblical period which have been discovered in the archaeological excavations in Israel is very small because of decay. The richest in wooden furniture and vessels are the mbii tombs in Jericho, where many tables, bowls, combs, jugs, and toilet boxes were preserved. When the Bible sharply criticizes idol worshipers, it indicates that they are worshipers of wood and stone, the work of men (Deut. 4:28). The use of wood in the construction of houses in Palestine is most variegated. It began with the building of huts from branches which were cut down and left in their natural state, and continues, until today, with the use of processed wood in the consolidation of frames of building and in the covering of wooden structures, as columns for reinforcing walls, for the roofing of clay, stone, or straw buildings, and for making doors and windows.

[Ze'ev Yeivin]

Wood Offerings

On nine different specified dates during the year, designated families brought wood offerings for the Temple sacrificial service. On the 15^th of *Av, the priests, levites, and all those not certain of their tribal descent were permitted to join the family designated for that day in bringing the wood offering (Ta'an. 4:5). One of the reasons given for the joyful celebrations on the 15^th of Av is that each year on this day felling trees for the altar was discontinued. The reason given is that after this time the strength of the sun lessens and its rays are no longer sufficiently strong to dry the fresh-cut logs (Ta'an. 31a). The wood most preferred for the altar was boughs of fig trees, nut trees, and oil trees (Tam. 2:3).

The rabbis praised the family of Salami Netofah for their efforts in getting wood to the Temple at a time when the ruling authorities placed guards on the roads to prevent Jews from bringing wood to the altar. This family conceived the stratagem of making the logs into ladders which they carried on their shoulders. When stopped by the guards the family explained that they were going to use the ladders to take down young pigeons from the dovecote. Once past the guards, they dismantled the ladders and brought the logs to Jerusalem (Ta'an. 28a).

bibliography:

W.M.F. Petrie and H. Mackay, Heliopolis, Kafr Ammr and Shurafa (1915), pl. xxv; H. Fechheimer, Kleinplastik der Aegypter (1921), p. 148; C. Singer et al., History of Technology, 1 (1954), 688, 700.

wood / woŏd/ • n. 1. the hard fibrous material that forms the main substance of the trunk or branches of a tree or shrub. ∎  such material when cut and used as timber or fuel: a large table made of dark, polished wood | best quality woods were used for joinery | [as adj.] a wood cross. ∎  a golf club with a wooden or other head that is relatively broad from face to back (often with a numeral indicating the degree to which the face is angled to loft the ball). ∎  a shot made with such a club. 2. (also woods) an area of land, smaller than a forest, that is covered with growing trees: a thick hedge divided the wood from the field a long walk in the woods.PHRASES: out of the wood (or woods) out of danger or difficulty.get wood vulgar slang have an erection.knock on wood said in order to prevent a confident statement from bringing bad luck: I haven't been banned yet, knock on wood. DERIVATIVES: wood·less adj.

wood Hard substance that forms the trunks of trees; it is the xylem which comprises the bulk of the stems and roots, supporting the plant. Wood consists of fine, cellular tubes arranged vertically within the trunk, which accounts for its grain. The relatively soft, light-coloured wood is called sapwood. The non-conducting, older, darker wood is called heartwood, and is generally filled with resin, gums, mineral salts, and tannin. The two chief types are softwoods from conifers, such as pine, and hardwoods from deciduous species, such as oak. Wood is commonly used as a building material, fuel, to make some types of paper, and as a source of charcoal, cellulose, essential oil, lignin, tannins, dyes, and sugar.