Hardwood


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Hardwood - short version

Wood from deciduous and broad-leaved tress such as ash, beech, birch and oak.



Hardwood - long version

The term 'hardwood' is used to describe 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.

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. 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 Paduk 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. Paduk is a hardwood commonly used for solid wood flooring. 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.



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