Wood is one of civilisation's earliest and most basic materials.
One of humanities first studies was to determine the properties
of the wood from different trees. To be able to select the
most suitable timber for your requirements, an understanding
of the structure and basic properties of wood is essential.
Wood's features, tree growth, and wood formation must be
understood. The differences in wood structure effecting
its material characteristics and function can then be investigated.
The physical and mechanical properties of wood is related
to its cell wall properties. It must also be realised that
the physical and mechanical properties of wood are not fixed
- they fall within boundaries or ranges - because wood is
a variable material .
Types: Hardwood and softwood
There are two main types of natural timber - hardwood and
The categories softwood and hardwood do not describe the
properties of the timber but refer to the types
of tree from which the woods are obtained.
Softwoods come from trees that possess seed-bearing
cones - known as coniferous trees. Coniferous trees are
evergreens - they keep their leaves and grow all year round
- and usually have needle-like leaves. Many softwood trees
take between 25 and 50 yrs to reach maturity - although
some have been known to be up to 4800 years old (the Great
Basin bristlecone pine in the USA). They tend to be less
expensive than hardwoods. Coniferous trees are adapted to
a wider range of climates than hardwoods - they occur naturally
from north of the artic circle in Finland right down to
the Equator in Sumatra - and usually can be found at higher
altitudes than hardwoods. In Australia, native conifers
can be found from north Queensland to Tasmania. (See
the section on Softwoods for more details).
Hardwoods come from broadleaved, flowering trees
(dicotyledonous angiosperms). The term has no reference
to the actual hardness of the wood. Angiosperms produce
a fruit or nut. Hardwood trees that are used commercially
for timber generally take longer than conifers to reach
maturity - up to 100 yrs or more. They grow in warmer climates
and tend to be more expensive than softwoods. (See the
section on Hardwoods for more details).
Softwoods are usually relatively uniform in their appearance
because 90% of softwood wood is composed of a single cell
type - the longitudinal tracheid. The tracheid's function
is to support the tree and to allow water conduction to
the leaves. The other 10% of softwoods are composed of ray
parenchyma. (Rays usually are only 1 cell wide). Some softwoods
also have small amounts of other cells. In softwoods, the
tracheid cell has two roles .
Follow this link to see views of the longitudinal
The photographs are taken with both a scanning
electron microscope and hand-lens ( large 183 kb image file).
Follow this link to see how tracheids
look from different sections through the log. When you arrive
at this hyperlink, click on "Radial view" (55
kb image file size) then "Tangential view"
(62 kb image file size) .
The distinguishing feature of hardwoods is the vessel element,
an open-ended cell. Hardwoods have longitudinal "vessels"
that transport solutions, "fibers" that perform the mechanical
support role, and "parenchyma" for storage. Fibres make
up the bulk of the wood. Hardwoods, being 'vessel-permeated',
therefore have a more complex appearance than softwoods.
In hardwoods, each type of cell has a specialist role .
Follow this link to see vessel
elements in hardwood .
When you follow this hyperlink, scroll down the webpage
to see the photographs.
General wood properties
Although the wood of all trees consists essentially of
cellulose fibres held together by lignin, different trees
produce woods with many different properties that make them
suitable for different purposes.
In the important section on general wood properties the
three distinct surfaces of wood will be explained: cross
section, radial, and tangential. Wood not only looks different
in cross section, radial, and tangential views, but it also
has considerably different properties depending upon its
Both hardwoods and softwoods can be formed into manufactured
boards (plywood, hardboard, MDF, chipboard). Manufactured
timber is processed by cutting up solid timber and putting
it back together in a variety of different ways. The main
reason for doing this is to end up with large flat sheets
of timber which are stronger, more stable and less expensive
than comparible sized timber. When a tree is milled (cut
up into usable sized pieces - like the ones you use in the
wood-shop), up to 40% is left as waste (sawdust and small
odd-sized pieces) so this waste material is manufactured
into wood product sheets. (See the section on Manfactured
boards for more details).
angiosperm: Flowering plants (seeds enclosed in
an ovary - flowering plant).
dicotyledonous: A flowering plant with two embryonic
seed leaves or cotyledons that usually appear at germination.
fibers: (Botany). One of the elongated, thick-walled
cells that give strength and support to plant tissue.
parenchyma: Thin-walled cells that remain capable
of cell division even when mature, constitutes the greater
part of leaves, roots, the pulp of fruits, and the pith
vessels: (Botany). One of the tubular conductive
structures of xylem, consisting of dead cylindrical cells
that are attached end to end and connected by perforations.
They are found in nearly all flowering plants.
xylem: The supporting and water-conducting tissue
of vascular plants, consisting primarily of tracheids and
vessels; woody tissue.
 Wheeler, Dr. E.A. (1997, June). North
Carolina State University: Wood Anatomy & Properties
[WWW Document] URL http://courses.ncsu.edu/classes/wps202001/202syl/wps202.html
(visited January, 2001).
Copyright D. L. Christiansen [Last updated
February 2001] Images: respective copyright owners noted/cited.
to Materials Technology - WOOD