What is Hardwood and Softwood
There are two main types of wood - softwood and hardwood.
Softwood and hardwood are terms that refer to the water-conducting cells in a living tree from which timber comes, and not to the hardness or softness of the wood itself. You can see the differences between the different cells when you look at wood samples through a microscope or under a powerful magnifying glass.
In softwoods, the water-conducting cells are known as xylem tracheids and are tapered in shape, while in hardwoods these cells are tubular-shaped and are known as xylem vessels.
Conifers are an example of gymnosperms - cone-producing plants. All conifer species are softwoods, including radiata pine, an introduced pine species grown in softwood plantations in southern New South Wales.
Angiosperms are flowering plants. Eucalypts are an example of angiosperms and are an example of a native hardwood species. Balsa wood, although a 'soft' wood, is also a hardwood.
Broad-leaved trees, like eucalypts and red cedar, are hardwood trees. Most Australian native timber trees are hardwoods. The wood of these trees is made up of two distinct types of cells, vessels and fibre cells.
Sap is carried upwards in large ducts known as vessels or pores. This start as wide cells with large cavities, arranged one above the other. In some cells the end walls break down to create long pipes running considerable distances. Vessels can usually be seen with the naked eye. Timbers with vessels are sometimes called pored timbers (hardwoods), and the arrangement of the vessels in a cross-section is a useful aid to identifying different timbers.
Strength in broad-leaved trees is imparted by other types of cells, called fibres. These are similar to conifer tracheids but are shorter in length (commonly about one millimetre long) and usually thicker-walled. Fibres make up the bulk of the wood in broad-leaved trees and, like tracheids, the walls of these cells are made of cellulose and neighbouring cells are held together by lignin.
Points to ponder
1. Why are the terms softwood and hardwood not really appropriate when used to describe different types of timber?
2. A large part of the world's timber trade and use of wood is based on conifers (softwood). Why do you think this is the case?
3. In parts of the Northern Hemisphere, wood from historic and archaeological sites has proved valuable in providing information about climate patterns of many centuries ago. How can wood provide information about climate patterns, in particular changes in climate patterns?
4. The sapwood of some trees is treated with preservatives before being used for some purposes. Why?
Hardwood does not need to be treated. Why?