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Beech is a popular temperate zone hardwood

Hardwood is wood from angiosperm trees (more strictly speaking non-monocot angiosperm trees). It may also be used for those trees themselves: these are usually broad-leaved; in temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen.

Hardwood contrasts with softwood which comes from conifer trees, which usually are not broad-leaved. Hardwoods are not necessarily harder than softwoods. In both groups there is an enormous variation in actual wood hardness, with the range in density in hardwoods completely including that of softwoods; some hardwoods (e.g. balsa) are softer than most softwoods, while yew is an example of a hard softwood. The hardest hardwoods are much harder than any softwood. There are about a hundred times as many hardwoods as softwoods.

Contents

Structure

SEM images showing the presence of pores in hardwoods (Oak, top) and absence in softwoods (Pine, bottom)

Hardwoods have a more complex structure than softwoods. The dominant feature separating "hardwoods" from softwoods is the presence of pores, or vessels[1]. The vessels may show considerable variation in size, shape of perforation plates (simple, scalariform, reticulate, foraminate), and structure of cell wall (e.g. spiral thickenings).

Common hardwoods

Common deciduous European and North American "hardwoods" include the oaks (Quercus spp.), beech (Fagus spp.), ash (Fraxinus spp.), maple (Acer spp.) and cherry (Prunus spp.). Examples of European evergreen trees that yield specialty hardwoods (used in small volumes) include holly (Ilex aquifolium), boxwood (Buxus sempervirens) and holm oak (Quercus ilex). Important tropical hardwoods include teak (Tectona grandis), mahogany (Swietenia spp.), ebony (Diospyros spp.) and lauan (Shorea spp.).

Applications

Hardwoods are employed in a large range of applications including: construction, furniture, flooring, cooking, utensils, etc. Solid hardwood joinery tends to be expensive compared to softwood. In the past, tropical hardwoods were easily available but the supply of some species such as Burma teak and mahogany is now becoming restricted due to over-exploitation. Cheaper "hardwood" doors, for instance, now consist of a thin veneer bonded to a core of softwood, plywood or medium-density fibreboard (MDF). Hardwoods can also be used in a variety of objects but mainly for furniture or musical instruments because of their density. Different species of hardwood lend themselves to different end uses or construction processes. This is due to the variety of characteristics apparent in different timbers including, density, grain, pore size, growth pattern, wood fibre pattern, flexibility and ability to be steam bent. For example, the interlocked grain of elm wood (Ulmus spp.) makes it suitable for the making of chair seats where the driving in of legs and other components can cause splitting in other woods.

Cooking

There is a correlation between density and calories/volume. This makes the denser hardwoods such as oak, cherry, and apple more suited for camp fires, cooking fires, and smoking meat as they tend to burn hotter and longer than softwoods such as pine or cedar.

Characteristics

The wood from these trees is generally harder. (That's where the name comes from.) Hardwoods reproduce by flowers. Hardwoods have broad leaves. Many lose their leaves every autumn and are dormant in the winter. [2]

See also

References

  1. ^ CRC Handbook of Materials Science, Vol IV, pg 15
  2. ^ http://www.ruthtrumpold.id.au/designtech/pmwiki.php?n=Main.TimberNew

Further reading

  • Schweingruber, F.H. (1990) Anatomie europäischer Hölzer—Anatomy of European woods. Eidgenössische Forschungsanstalt für Wald, Schnee und Landscaft, Birmensdorf (Hrsg,). Haupt, Bern und Stuttgart.
  • Timonen, Tuuli (2002). Introduction to Microscopic Wood Identification. Finnish Museum of Natural History, University of Helsinki.
  • Wilson, K., and D.J.B. White (1986). The Anatomy of Wood: Its Diversity and variability. Stobart & Son Ltd, London.

External links

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