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Bark of mature Mango (Mangifera India) showing characteristic lichen growth, Kolkata, India

Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term.[1] It overlays the wood and consists of the inner bark and the outer bark. The inner bark, which in older stems is living tissue, includes the innermost area of the periderm. The outer bark in older stems, includes the dead tissue on the surface of the stems, along with parts of the innermost periderm and all the tissues on the outer side of the periderm. The outer bark on trees is also called the rhytidome. Products used by people that are derived from bark include: spices and other flavorings, tannin, resin, latex, medicines, poisons, various hallucinatory chemicals and cork. Bark has been used to make cloths, canoes, ropes and used as a surface for paintings and map making.[2] A number of plants are also grown for their attractive or interesting bark colorations and surface textures or their bark is used as landscape mulch.[3][4]

Contents

Periderm

Often a secondary covering called the periderm forms on small woody stems and many non woody plants, which is composed of cork (phellem), the cork cambium (phellogen), and the phelloderm. The periderm forms from the phellogen which serves as a lateral meristem. The periderm replaces the epidermis, and acts as a protective covering like the epidermis. Mature phellem cells have suberin in their walls to protect the stem from desiccation and pathogen attack. Older phellem cells are dead, as is the case with woody stems. The skin on the potato tuber (which is an underground stem) constitutes the cork of the periderm.[5] [6]

In woody plants the epidermis of newly grown stems is replaced by the periderm later in the year. As the stems grow a layer of cells form under the epidermis, called the cork cambium, these cells produce cork cells that turn into cork. A limited number of cell layers may form interior to the cork cambium, called the phelloderm. As the stem grows, the cork cambium produces new layers of cork which are impermeable to gases and water and the cells outside of the periderm, namely the epidermis, cortex and older secondary phloem die. [7]

Within the periderm are lenticels, which form during the production of the first periderm layer. Since there are living cells within the cambium layers that need to exchange gases during metabolism, these lenticels, because they have numerous intercellular spaces, allow gaseous exchange with the outside atmosphere. As the bark develops, new lenticels are formed within the cracks of the cork layers.

Rhytidome

Living tree bark enveloping barbed wire

The rhytidome is the most familiar part of bark, it is the outer layer that covers the trunks of trees. It is composed mostly of dead lignified cells and is produced by the formation of multiple layers of periderm, cortical and phloem tissue.[8] It is generally thickest and most distinctive at the trunk or bole (The area from the ground to where the main branching starts) of the tree.

Uses

Cork, sometimes confused with bark in colloquial speech, is the outermost layer of a woody stem, derived from the cork cambium. It serves as protection against damage from parasites, herbivorous animals and diseases, as well as dehydration and fire. Cork can contain antiseptics like tannins, that protect against fungal and bacterial attacks that would cause decay.

Backpack made of birch bark.

In some plants, the bark is substantially thicker, providing further protection and giving the bark a characteristically distinctive structure with deep ridges. In the cork oak (Quercus suber) the bark is thick enough to be harvested as a cork product without killing the tree. Some barks can be removed in long sheets; the smooth surfaced bark of birch trees has been used as a covering in the making of canoes, as the drainage layer in roofs, for shoes, backpacks etc. The most famous example of using birch bark for canoes is the birch canoes of North America.[9]

The bark of some trees is edible; in Finland, pine bread is made from rye to which the toasted and ground innermost layer of pine bark is added, the Sami people of far northern Europe used large sheets of Pinus sylvestris bark that were removed in the spring, prepared and stored for use as a staple food resource and the inner bark was eaten fresh, dried or roasted.[10] Bark contains strong fibres known as bast, and there is a long tradition in northern Europe of using bark from coppiced young branches of the small-leaved lime (Tilia cordata) to produce cordage and rope, used for example in the rigging of Viking age longships.[11]

Among the commercial products made from bark are cork, cinnamon, quinine[12] (from the bark of Cinchona)[13] and aspirin (from the bark of willow trees). The bark of some trees notably oak (Quercus robur) is a source of tannic acid, which is used in tanning. Bark chips generated as a by-product of lumber production, are often used in bark mulch in western North America. Bark is important to the horticultural industry since in shredded form it is used for plants that do not thrive in ordinary soil, such as epiphytes.

Bark chip extraction

Wood Adhesives from Bark-Derived Phenols: Wood Bark has lignin content and when it is pyrolyzed (subjected to high temperatures in the absence of oxygen), it yields a liquid bio-oil product rich in natural phenol derivatives. The phenol derivatives are isolated and recovered for application as a replacement for fossil-based phenols in phenol-formaldehyde (PF) resins used in Oriented Strand Board (OSB) and plywood.

Bark removal

Patches of Bark naturally flaking off the bottom of Roystonea regia palm trunk, Kolkata, India

Cut logs used for the production of lumber or even log cabins generally have the bark removed, either just before cutting or for curing. Such logs and even trunks and branches found in their natural state of decay in forests, where the bark has fallen off, are said to be decorticated.

A number of living organisms live in or on bark, including insects,[14] fungi and other plants like mosses , algae and other vascular plants. Many of these organisms are pathogens or parasites but some also have symbiotic relationships.

Bark repair

Alder bark (Alnus glutinosa) with characteristic lenticels and abnormal lenticels on callused areas.
Sun scald damage on Sitka spruce

The degree to which trees are able to repair gross physical damage to their bark is very variable. Some are able to produce a callus growth which heals over the wound rapidly, but leaves a clear scar, whilst others such as oaks do not produce an extensive callus repair.

Frost crack and Sun scald (flora) are examples of damage found on tree bark which trees can repair to a degree, depending on the severity.

Gallery

See also

References

  1. ^ Raven, Peter H.; Evert, Ray F.; Curtis, Helena (1981), Biology of Plants, New York, N.Y.: Worth Publishers, pp. 641, ISBN 0879011327, OCLC 222047616 
  2. ^ Taylor, Luke. 1996. Seeing the Inside: Bark Painting in Western Arnhem Land. Oxford Studies in Social and Cultural Anthropology. Oxford: Clarendon Press.
  3. ^ Sandved, Kjell Bloch, Ghillean T. Prance, and Anne E. Prance. 1993. Bark: the Formation, Characteristics, and Uses of Bark around the World. Portland, Or: Timber Press.
  4. ^ Vaucher, Hugues, and James E. Eckenwalder. 2003. Tree Bark: a Color Guide. Portland: Timber
  5. ^ Artschwager, E. 1924. Studies on the potato tuber. J. Agr. Res. 27:809-835.
  6. ^ Peterson, R.L. and W.G. Barker. 1979. Early tuber development from explanted stolon nodes of Solanum tuberosum var. Kennebec. Bot. Gaz. 140:398-406.
  7. ^ Mauseth, James D. (2003), "Botany: an Introduction to Plant Biology", Isbn 0763721344: 229 
  8. ^ Dickison, WC. 2000. Integrative Plant Anatomy, Academic Press, San Diego, 186-195.
  9. ^ Adney, Tappan, and Howard Irving Chapelle. 1964. The Bark Canoes and Skin Boats of North America. Washington: Smithsonian Institution.
  10. ^ Zackrisson, O.; Östlund, L.; Korhonen, O.; Bergman, I. (200), [http://cat.inist.fr/?aModele=afficheN&cpsidt=1559092 === Mechanical bark processing === "The ancient use of Pinus sylvestris L. (scots pine) inner bark by Sami people in northern Sweden, related to cultural and ecological factors = Ancienne usage d\'écorce de Pinus sylvestris L. (Pin écossais) par les peuples Sami du nord de la Suède en relation avec les facteurs écologiques et culturels"], Vegetation History and Archaeobotany 9 (2): 99–109, http://cat.inist.fr/?aModele=afficheN&cpsidt=1559092 === Mechanical bark processing === 
  11. ^ Myking T., Hertzberg, A. and Skrøppa, T. (2005) History, manufacture and properties of lime bast cordage in northern Europe. Forestry 78(1): 65-71; doi:10.1093/forestry/cpi006
  12. ^ Duran-Reynals, Marie Louise de Ayala. 1946. The Fever Bark Tree; the Pageant of Quinine. Garden City, N.Y.: Doubleday.
  13. ^ Markham, Clements R. 1880. Peruvian Bark. A Popular Account of the Introduction of Chinchona Cultivation into British India. London: J. Murray.
  14. ^ Lieutier, François. 2004. Bark and Wood Boring Insects in Living Trees in Europe, a Synthesis. Dordrecht: Kluwer Academic Publishers.

Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also bark

German

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German Wikipedia has an article on:
Bark (Schiff)

Wikipedia de

Noun

Bark f. (genitive Bark, plural Barken)

  1. bark (three-masted vessel)

Simple English

File:Pine
the bark of a Monterey Pine

Bark is the covering of the stems of woody plants, like trees. Bark protects the tree. Bark of different plants and trees can look very different, it can be rough or smooth and can have different colors.

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