|Wood is an exceedingly complex organic material. Scientists have been studying its structure for centuries. The fields of wood anatomy and physics are immense and growing. In order to keep this book focused on structural applications, the wood anatomy presented will be superficial, even below the detail level of high school biology. Only those features and orientations of wood’s internal structure that most significantly affect its behavior as a building material will be covered.|
HARDWOODS AND SOFTWOOD
The terms hardwood and softwood, while commonly used and understood, are often misnomers. Hardwoods such as balsa and aspen are quite soft, while softwoods such as white pine and true fir are quite hard. The less common, but more precise, terms deciduous and coniferous are not universally applicable either. Deciduous (hardwood) trees are defined as those that lose their broad leaves annually, a rule violated every year in the tropics. Coniferous(softwood) trees, on the other hand, are not supposed to lose their leaves (needles) and should have seeds in cones. Again, there are species commonly recognized as softwoods that ignore this definition. But, the hardwood/softwood distinction is so widespread that time spent disputing it is largely wasted.
There are other differences between the two basic tree types. Internal structure in the softwoods is far simpler than in the hardwoods. There are only 650 softwood species, and they can be found in vast tracts, often containing only one species. There are more than 250,000 hardwood species, however, and they are widely scattered and interspersed.
The entire issue of softwood, versus hardwood is largely an academic one, however, as far as the structural applications of this book are concerned. The majority of structural timber requirements are filled with softwoods. Hardwoods are mostly used for fuel, railroad ties, pallets, furniture, and paneling, and many other non-structural products. Exceptions to this pattern are the older structures built amid the hardwood forests of the eastern United States.