Hardwoods are generally broad-leaved (deciduous) trees, which often lose their leaves at the end of each growing season. The cell structure of hardwoods is more complex than that of softwoods with thick-walled cells, called fibres, providing the structural support and thin-walled cells, called vessels, providing the medium for food conduction. Due to the necessity to grow new leaves every year the demand for sap is high and in some instances larger vessels may be formed in the springwood, these are referred to as 'ring-porous' woods such as in oak and ash. When there is no definite growing period the pores tend to be more evenly distributed, resulting in 'diffuse-porous' woods such as in poplar and beech. Examples of the UK grown hardwoods include oak, beech, ash, alder, birch, maple, poplar and willow. Hardwood characteristics

• Hardwoods grow at a slower rate than softwoods, which generally results in a timber of high density and strength, which takes time to mature, over 100 years in some instances.

• There is less dependence on preservatives for durability qualities.

• Due to the time taken to mature and the transportation costs of hardwoods, as most are tropical, they tend to be expensive in comparison with softwoods.

British Standard BS 5359:1991 [3] provides a list of some 500 timbers of economic interest in the United Kingdom and tabulates softwoods and hardwoods including their standard names, botanical names/species type and also, where relevant, their alternative commercial names with sources of supply and average densities.

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