A good woodworker need not be an expert botanist, but it does help if you have a basic knowledge of trees. Knowing how wood 'grows' will help in all aspects of woodworking, especially when selecting your wood.
The ability to select the best material will avoid having to deal with potential problems as the wood is machined, and avoiding defects that may even make it to the finished product.
Wood in its raw material form comes from trees which are the most prominent members of the plant kingdom. A tree is comprised of a root system, a truck (or bole), branches, and foliage. It is the trunk of the tree that most of our wood is derived from.
What is wood exactly?
The cellular structure of wood is made from cellulose bonded together with a chemical called lignin. The cellulose forms the cell walls while the lignin acts as the glue that holds everything together, while at the same time allowing water to pass through to the cells.
It is the size and shape and density of the cells that give wood its characteristics of texture and grain pattern, while grain pattern is related to the growth direction of the cell fibers.
Softwoods and Hardwoods
Gymnosperms and Angiosperms as they are respectively called scientifically give us the two groupings of softwoods and hardwoods. Gymnosperms are conifers or needle bearing trees, and angiosperms are broad leaf bearing (and losing) trees.
However, these terms can be misleading as some softwoods are harder than certain hardwoods. In general, these labels are reliable, but one notable example of a soft 'hardwood' is balsa wood.
Softwood lumber is mostly used in building structures. It is faster growing and therefore cheaper, whereas hardwood lumber grows more slowly and denser than softwood. Most furniture is made from hardwood lumber.
Within the Tree
An important part of woodworking is knowing how wood behaves as it machined and dried. The outer layer is the bark of the tree which serves as protection. Just below the bark is the vascular cambium or bast. This is the part of the tree that conducts the nutrients and sugars the tree needs to survive. The cambium layer is also the only layer that grows thickness in the tree and is what creates the annual growth rings.
The sapwood layer conducts the sap upwards from the roots. Some species of tress will have sapwood that is paler than the heartwood, while other trees will not have this distinction.
Depending on the species, either the sapwood or the heartwood will be the 'valuable' part. The heartwood makes up the bulk of the tree. This part is no longer living, but supplies the strength of the tree.
As the tree grows, the sapwood becomes heartwood as new layers of sapwood are added each year. The pith, which is the oldest part of the tree is weak and is usually not usable to a woodworker.
The lumber that is derived from a tree will also have different working properties depending on how it was sawed. There are numerous methods of sawing lumber into boards, the most often cuts are the quarter sawn, rift sawn and flat sawn types. Each type of cut will affect the yield of lumber from a whole tree and will also affect the pattern of the growth rings on the final board.
Often times, trees with special wood characteristics are sawn in a specific manner in order to highlight those characteristics. One such example is the common red oak which shows off it medullary rays when quarter sawn.
Unlike other trades, most of the material for woodworkers is not uniform, but comes from a living organism and will exhibit all kinds of different features even within closely related tree species. It takes time to learn all the distinctions, but that is where the artistry comes in. And being able to choose that perfect piece of wood to be displayed into the finished product adds great enjoyment to the skill of woodworking.