Question

What are the different types of timber varieties encountered in forensic cases.

Answer 1

Identification of Timber: Timber has a variety of form which enables it to serve a variety of uses and contributes to its pleasing aesthetic appearance. However, the variability also means that there is lack of uniformity, which is a disadvantage when the timber is used for engineering applications. Timber identification aims at naming the species of tree from which the unknown sample has been cut, thus providing a means of assessing much useful information about the timber which would otherwise be unavailable.

There are two basic types of wood: 

1) Softwoods: are from trees of Sub-phylum Gymnospermae – Order Coniferales - the conifers. The trees do not have true flowers, seeds are naked (not enclosed in any way) and borne on a scale of a cone. Leaves are usually needle-like and evergreen. 

2) Hardwoods: are from trees of Sub-phylum Angiospermae – Class Dicotyledae - the flowering trees – seeds are produced inside an ovary or fruit. Leaves are typically broad and flat.

Viewing the microscopic characters of the wood can be carried out using the following tools:

A magnifying glass which will give 4 to 20 times magnification - usually sufficient for hardwoods but not for softwoods

A light microscope gives 5 to 400 times magnification and is the prime tool for wood identification

Scanning electron microscopy (SEM) gives up to 100,000 times magnification, 3D views, no colour.

Important identifying features for softwoods:

In woods from regions with strong seasonal differences, there are noticeable seasonal changes between the tracheids that form the latewood and the earlywood whereas in woods tropical regions, tracheid size is basically the same throughout the growth ring.

Presence of resin canals - present in Pinus, Larix (larch); Picea (spruce) and Pseudotsuga (douglas fir)

Bordered pit arrangement (uniseriate is common; multiseriate staggered in Araucariaceae; multiseriate opposite in Sequoia)

Important identifying features for hardwoods:

In woods from regions with strong seasonal differences, there are obvious seasonal changes in vessel (pore) size.

In woods from tropical regions, vessel (pore) size is often the same throughout the growth ring

Vessels (pores) can be solitary or can be clustered into “radial multiples”.

Pore groups can be distributed evenly or arranged in radial, diagonal lines, or tangential lines.