“How much wood would a woodchuck chuck, if a woodchuck could chuck wood?” asks the familiar tongue-twister, to which the reply would have to be, in parts of southern Saskatchewan, “Not much.” The prairies just aren’t known for their abundance of trees.
Northern Saskatchewan, however, is an entirely different matter. My continuing travels around the province on the Prairie Opera school tour have now taken me as far north as LaRonge, where a woodchuck could chuck wood to his little heart’s content, and still have lots of wood left over.
But just what is it the woodchuck would chuck? What is wood?
Well, of course, wood is what the trunk of a tree is made out of, but that’s hardly a sufficient answer. Like a boring beetle (although, in general, “boring” is something I try to avoid as a columnist, this time I’ll make an exception), let us penetrate the tree’s bark and look at what’s inside.
Wood starts out life soft and growing, its veins full of vital fluids, and ends up hard and stultified, its veins full of gunk, from which I could draw a really depressing metaphor about the human condition if I weren’t in a good mood. Wood consists primarily of fine tubes which carry water and dissolved minerals from the tree’s roots to its leaves. It’s these fine tubes that give wood its grain when its cut.
However, most of the wood cells in a tree trunk are dead. Trees grow upward only at their uppermost tip; otherwise, they only grow in width. Each year new wood is laid down in the cambium, a thin layer surrounding the trunk. (It’s this new annual growth that produces the characteristic rings seen when a tree trunk is cut in cross-section.) Only these new cells are alive; cells from previous year’s growth are dead. However, for a few years the tubes in the old wood continue to conduct water to the rest of the tree. After that, the tubes become so clogged with waste products, such as tannins, dyes and resins, that they can no longer conduct water.
Wood that is still conducting water is called sapwood; wood that no longer can is called heartwood. The heartwood’s main function is to give the tree strength and rigidity. It also makes better lumber because it is usually drier, and, due to the aforementioned tannins, dyes and resins, both has a richer color and is more resistant to decay.
Wood is made primarily of cellulose and lignin. Cellulose consists of many glucose molecules linked together in long chains, which produces threadlike fibers, that wind together so tightly that wood can be as strong as an equivalent thickness of steel.
Exactly how strong wood is depends on the kind of tree it comes from, whether its sapwood or heartwood, and how well seasoned it has been. Wood is divided into hardwoods (woods from broad-leaved trees) and softwoods (wood from confierous trees), but that labelling is rather arbitrary, in that wood from some coniferous trees can actually be harder than wood from some broadleaved trees. A better classification might be porous and non-porous: hardwoods have large pores that conduct sap, whereas softwoods don’t, and often have resin ducts, instead.
Even if hardwood isn’t necessarily harder than softwood, the fact that wood is hard is one reason it has been used for thousands of years for building things. Wood is also durable–when protected from parasites and the elements, it can last for centuries virtually unchanged (some wooden artifacts survive from Roman times, for example). The most destructive organisms that attack wood are the fungi that cause so-called dry rot (a rather misleading name since it only occurs when wood is damp). All sapwood is susceptible to this form of decay, but the heartwood of some species–walnut and cedar, for example–is resistant. Other woods are resistant to other parasites, such as marine borers and termites, and therefore find use in specialized environments where such parasites are a problem. Sometimes wood is impregnated with zinc chloride, better known as creosote, to keep parasites from chowing down on it.
Wood conducts heat poorly, which has made it useful as a building material in cold climates. At the same time, it burns very well, which has made it valuable as a fuel. Almost any kind of wood will burn, but in general, denser woods tend to burn hotter and longer. Some types of softwood burn very rapidly because they contain flammable resins.
Whether it’s needed for building or fuel, wood is most useful once it has been seasoned, or dried. Freshly cut wood contains a lot of water, amounting to as much as one third to more than one-half of its total weight. Seasoning, which can be done either by air-drying (which can take months) or in a kiln (a matter of days), makes the wood more resistant to decay and lighter and therefore easier to ship. As well, wood changes shape during drying, a change which should be completed before the wood is cut.
Once it’s dried, some wood ends up wet again, because it’s made into a boat. Most wood floats (there are a few extremely dense types that don’t) because it contains so many air-filled pores.
In addition to being used for building things and to make paper, wood is valuable as a source of chemicals. The artifical fiber rayon is made from cellulose; much of it comes from cotton, but an increasing amount of it comes from wood. Lignin, which used to be discarded when cellulose was extracted, is now used in the manufacture of plastics and as a culture medium for yeast. Wood can also be treated to produce sugars and alcohols.
Two of the newest wood products are called impreg and compreg. Impreg is made by impregnating the wood with certain chemicals, then heating the wood so that the chemicals react with the wood cells to form a plastic. Impreg is very resistant to decay and is somewhat denser than wood, though not much stronger.
Compreg is by compressing the impregnated wood while the plastic is forming. Compreg is much denser than all but the densest woods (it doesn’t float), it’s many times harder, and it’s also stronger.
Whether in its traditional form or in new, technologically-mutated forms, wood continues to be vital to our civilization. Just because it grows all over the northern two-thirds of the province is no reason to take it for granted.
And somebody stop that darn animal from the tongue-twister. This stuff is obviously far too valuable to chuck!
